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{{Infobox particle
| name = Higgs boson
| image = [[File:Candidate Higgs Events in ATLAS and CMS.png|frameless]]
| caption = Candidate Higgs boson events from [[particle collision|collision]]s between [[proton]]s in the [[LHC]]. The top event in the [[Compact Muon Solenoid|CMS]] experiment shows a decay into two [[photon]]s (dashed yellow lines and green towers). The lower event in the [[ATLAS experiment|ATLAS]] experiment shows a decay into four [[muon]]s (red tracks).<ref group="Note">Note that such events also occur due to other processes. Detection involves a [[statistically significant]] excess of such events at specific energies.</ref>
| composition = [[Elementary particle]]
| statistics = [[Bosonic]]
| interaction =
| particle =
| antiparticle =
| status = A Higgs boson of mass ~125 GeV has been tentatively confirmed by CERN on 14 March 2013,<ref name="CERN March 2013">
{{cite web
|last=O'Luanaigh |first=C.
|date=14 March 2013
|title=New results indicate that new particle is a Higgs boson
|url=http://home.web.cern.ch/about/updates/2013/03/new-results-indicate-new-particle-higgs-boson
|publisher=[[CERN]]
|accessdate=2013-10-09
}}</ref><ref name=nbc14032013>
{{cite news
  |last=Bryner |first=J.
  |date=14 March 2013
  |title=Particle confirmed as Higgs boson
  |url=http://science.nbcnews.com/_news/2013/03/14/17311477-particle-confirmed-as-higgs-boson
  |work=[[NBC News]]
  |accessdate=2013-03-14
}}</ref><ref name="Huffington 14 March 2013">
{{cite news
  |last=Heilprin |first=J.
  |date=14 March 2013
  |title=Higgs Boson Discovery Confirmed After Physicists Review Large Hadron Collider Data at CERN
  |url=http://www.huffingtonpost.com/2013/03/14/higgs-boson-discovery-confirmed-cern-large-hadron-collider_n_2874975.html?icid=maing-grid7%7Cmain5%7Cdl1%7Csec1_lnk2%26pLid%3D283596
  |work=[[The Huffington Post]]
  |accessdate=2013-03-14
}}</ref> although unclear as yet which model the particle best supports or whether multiple Higgs bosons exist.<ref name="nbc14032013" /><br />''(See: [[#Current status|Current status]])''
| theorised = [[Robert Brout|R. Brout]], [[François Englert|F. Englert]], [[Peter Higgs|P. Higgs]], [[Gerald Guralnik|G. S. Guralnik]], [[C. R. Hagen]], and [[T. W. B. Kibble]] (1964)
| discovered = Previously unknown boson confirmed to exist on 4 July 2012, by the [[ATLAS experiment|ATLAS]] and [[Compact Muon Solenoid|CMS]] teams at the [[Large Hadron Collider]]; tentatively confirmed as a Higgs boson of some kind on 14 March 2013 (see above).
| symbol = H<sup>0</sup>
| mass = {{nowrap|125.3 ± 0.4 (stat) ± 0.5 (sys) GeV/''c''<sup>2</sup>}},<ref name=cms0731>
{{Cite journal
  |author=[[Compact Muon Solenoid|CMS collaboration]]
  |coauthors=<!-- -->
  |year=2012
  |title=Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC
  |journal=[[Physics Letters B]]
  |volume=716 |issue=1 |pages=30–61
  |arxiv=1207.7235
  |bibcode=2012PhLB..716...30C
  |doi=10.1016/j.physletb.2012.08.021
  |ref=harv
}}</ref> {{nowrap|126.0 ± 0.4 (stat) ± 0.4 (sys) GeV/''c''<sup>2</sup>}}<ref name=atlas0731>
{{Cite journal
  |author=[[ATLAS experiment|ATLAS collaboration]]
  |year=2012
  |title=Observation of a New Particle in the Search for the Standard Model Higgs Boson with the ATLAS Detector at the LHC
  |journal=[[Physics Letters B]]
  |volume=716 |issue=1 |pages=1–29
  |arxiv=1207.7214
  |bibcode=2012PhLB..716....1A
  |doi=10.1016/j.physletb.2012.08.020
  |ref=harv
}}</ref>
| mean_lifetime = {{val|1.56|e=-22|u=s}}<ref name="meanlife" group="Note"/> (predicted in the [[Standard Model]])
| decay_particle = (observed) W and Z bosons, two photons. (Others still being studied)
| electric_charge = 0
| color_charge = 0
| spin = 0 (tentatively confirmed at 125 GeV)<ref name="CERN March 2013" />
| parity = +1 (tentatively confirmed at 125 GeV)<ref name="CERN March 2013" />
| num_spin_states =
}}
The '''Higgs boson''' or '''Higgs particle''' is an [[elementary particle]] initially [[1964 PRL symmetry breaking papers|theorised in 1964]],<ref name=nbc14032013/><ref name="NYT-20130305">
{{cite news
|last=Overbye |first=D.
|date=5 March 2013
|title=Chasing The Higgs Boson
|url=http://www.nytimes.com/2013/03/05/science/chasing-the-higgs-boson-how-2-teams-of-rivals-at-CERN-searched-for-physics-most-elusive-particle.html
|work=[[The New York Times]]
|accessdate=2013-03-05
}}</ref> whose discovery was announced at [[CERN]] on 4 July 2012.<ref name="discovery"/> The discovery has been called "monumental"<ref name=Mureika>
{{cite web
|date=7 August 2012
|title=Q&A: Prof. Jonas Mureika on the Higgs Boson
|url=http://www.lmu.edu/Page85725.aspx
|work=The Buzz
|publisher=[[Loyola Marymount University]]
|accessdate=2012-12-09
|quote=It's certainly a monumental milestone for physics.
}}</ref><ref name=ScienceNews>
{{cite news
|last=Siegfried |first=T.
|date=20 July 2012
|title=Higgs Hysteria
|url=http://www.sciencenews.org/view/generic/id/342408/title/Blog_Higgs_hysteria
|newspaper=[[Science News]]
|accessdate=2012-12-09
|quote=In terms usually reserved for athletic achievements, news reports described the finding as a monumental milestone in the history of science.
}}</ref> because it appears to confirm the existence of the '''Higgs field''',<ref name="OnyisiFAQ">
{{cite web
|last=Onyisi |first=P.
|date=23 October 2012
|title=Higgs boson FAQ
|url=https://wikis.utexas.edu/display/utatlas/Higgs+boson+FAQ
|publisher=[[University of Texas]] ATLAS group
|accessdate=2013-01-08
|quote=The Higgs field is extremely important in particle physics.
}}</ref><ref name="strasslerFAQ2">
{{cite web
|last=Strassler |first=M.
|date=12 October 2012
|title=The Higgs FAQ 2.0
|url=http://profmattstrassler.com/articles-and-posts/the-higgs-particle/the-higgs-faq-2-0/
|work=ProfMattStrassler.com
|accessdate=2013-01-08
|quote=[Q] Why do particle physicists care so much about the Higgs particle?<br />[A] Well, actually, they don’t. What they really care about is the Higgs ''field'', because it is ''so'' important. [emphasis in original]
}}</ref> which is pivotal to the [[Standard Model]] and other theories within [[particle physics]]. It would explain [[mass generation|why some fundamental particles have mass]] when the [[symmetry (physics)|symmetries]] controlling their interactions should require them to be massless, and why the [[weak force]] has a much shorter range than the [[electromagnetic force]]. The discovery of a Higgs boson should allow physicists to finally validate the last untested area of the Standard Model's approach to fundamental particles and forces, guide other theories and discoveries in particle physics, and potentially lead to developments in [[Physics beyond the Standard Model|"new" physics]].<ref>
{{cite web
|date=13 December 2011
|title=The Higgs boson: Evolution or revolution?
|url=http://press.web.cern.ch/backgrounders/higgs-boson-evolution-or-revolution
|publisher=[[CERN]]
|accessdate=2012-07-18
}}</ref>
 
This [[unanswered questions in physics|unanswered question]] in fundamental physics is of such importance<ref name="OnyisiFAQ" /><ref name="strasslerFAQ2" /> that it led to a [[Search for the Higgs boson|search of more than 40 years]] for the Higgs boson and finally the construction of one of the world's most [[List of megaprojects#Science projects|expensive and complex experimental facilities]] to date, the [[Large Hadron Collider]],<ref name="Strassler article">
{{cite web
|last=Strassler |first=M.
|date=8 October 2011
|title=The Known Particles&nbsp;– If The Higgs Field Were Zero
|url=http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-known-apparently-elementary-particles/the-known-particles-if-the-higgs-field-were-zero/
|work=ProfMattStrassler.com
|accessdate=13 November 2012
|quote=The Higgs field: so important it merited an entire experimental facility, the Large Hadron Collider, dedicated to understanding it.
}}</ref> able to create Higgs bosons and other particles for observation and study. On 4 July 2012, it was announced that a previously unknown particle with a mass between 125 and {{val|127|ul=GeV/c2}} (134.2 and 136.3 [[Atomic mass unit|amu]]) had been detected; physicists suspected at the time that it was the Higgs boson.<ref name="dieter July 2012">
{{cite news
|last=Biever |first=C.
|date=6 July 2012
|title=It's a boson! But we need to know if it's the Higgs
|url=http://www.newscientist.com/article/dn22029-its-a-boson-but-we-need-to-know-if-its-the-higgs.html
|accessdate=2013-01-09
|newspaper=[[New Scientist]]
|quote='As a layman, I would say, I think we have it,' said Rolf-Dieter Heuer, director general of CERN at Wednesday's seminar announcing the results of the search for the Higgs boson. But when pressed by journalists afterwards on what exactly 'it' was, things got more complicated. 'We have discovered a boson – now we have to find out what boson it is'<br />Q: 'If we don't know the new particle is a Higgs, what do we know about it?' We know it is some kind of boson, says Vivek Sharma of CMS [...]<br />Q: 'are the CERN scientists just being too cautious? What would be enough evidence to call it a Higgs boson?' As there could be many different kinds of Higgs bosons, there's no straight answer.<br />[emphasis in original]
}}{{dead link|date=November 2013}}</ref><ref name=ScienceNews /><ref name="CERN Nov 2012">
{{cite web
|last=Del Rosso |first=A.
|date=19 November 2012
|title=Higgs: The beginning of the exploration
|url=http://cds.cern.ch/record/1494477?ln=en
|work=[[CERN Bulletin]]
|issue=47–48
|accessdate=2013-01-09
|quote=Even in the most specialized circles, the new particle discovered in July is not yet being called the “Higgs boson". Physicists still hesitate to call it that before they have determined that its properties fit with those the Higgs theory predicts the Higgs boson has.
}}</ref> By March 2013, the particle had been proven to behave, interact and decay in many of the ways predicted by the Standard Model, and was also tentatively confirmed to have positive [[Parity (physics)|parity]] and zero [[Spin (physics)|spin]],<ref name="CERN March 2013" /> two fundamental attributes of a Higgs boson. This appears to be the first elementary [[scalar boson|scalar particle]] discovered in nature.<ref name="WSJ 14 March 2013">
{{cite news
|last=Naik |first=G.
|date=14 March 2013
|title=New Data Boosts Case for Higgs Boson Find
|url=http://online.wsj.com/article/SB10001424127887324077704578359850108689618.html
|accessdate=2013-03-15
|newspaper=[[The Wall Street Journal]]
|quote='We've never seen an elementary particle with spin zero,' said Tony Weidberg, a particle physicist at the University of Oxford who is also involved in the CERN experiments.
}}</ref> More data is needed to know if the discovered particle exactly matches the predictions of the Standard Model, or whether, as predicted by some theories, multiple Higgs bosons exist.<ref name="Huffington 14 March 2013" />
 
The Higgs boson is named after [[Peter Higgs]], one of [[1964 PRL symmetry breaking papers|six physicists who, in 1964]], proposed [[Higgs mechanism|the mechanism]] that suggested the existence of such a particle. Although Higgs's name has come to be associated with this theory, several researchers between about 1960 and 1972 each independently developed different parts of it. In mainstream media the Higgs boson has often been called the "God particle", from [[The God Particle: If the Universe Is the Answer, What Is the Question?|a 1993 book on the topic]]; the nickname is strongly disliked by many physicists, including Higgs, who regard it as inappropriate [[sensationalism]].<ref name="ISample29052009">{{cite news
|last=Sample |first=I.
|date=29 May 2009
|title=Anything but the God particle
|url=http://www.guardian.co.uk/science/blog/2009/may/29/why-call-it-the-god-particle-higgs-boson-cern-lhc
|work=[[The Guardian]]
|accessdate=2009-06-24
}}</ref><ref name="NatPost">
{{cite web
|last=Evans |first=R.
|date=14 December 2011
|title=The Higgs boson: Why scientists hate that you call it the 'God particle'
|url=http://news.nationalpost.com/2011/12/14/the-higgs-boson-why-scientists-hate-that-you-call-it-the-god-particle/
|work=[[National Post]]
|accessdate=2013-11-03
}}</ref> In 2013 two of the original researchers, Peter Higgs and [[François Englert]], were awarded the [[Nobel Prize in Physics]] for their work and prediction<ref>
{{cite news
|last=Overbye |first=D.
|date=8 October 2013
|title=For Nobel, They Can Thank the 'God Particle'
|url=http://www.nytimes.com/2013/10/09/science/englert-and-higgs-win-nobel-physics-prize.html?_r=3&
|newspaper=[[The New York Times]]
|accessdate=2013-11-03
}}</ref> (Englert's co-researcher [[Robert Brout]] had died in 2011).
 
In the Standard Model, the Higgs particle is a [[boson]] with no [[spin (physics)|spin]], [[electric charge]], or [[color charge]]. It is also very unstable, [[particle decay|decaying]] into other particles almost immediately. It is a [[excited state|quantum excitation]] of one of the four components of the Higgs field. The latter constitutes a [[scalar field|scalar]] [[field (physics)|field]], with two neutral and two electrically charged components, and forms a complex [[doublet (physics)|doublet]] of the [[weak isospin]] [[SU(2)]] symmetry. The field has a "[[Mexican hat potential|Mexican hat]]" shaped potential with nonzero strength everywhere (including otherwise empty space) which in its [[vacuum state]] breaks the weak isospin symmetry of the electroweak interaction. When this happens, three components of the Higgs field are "absorbed" by the SU(2) and U(1) [[gauge boson]]s (the "[[Higgs mechanism]]") to become the longitudinal components of the [[mass generation|now-massive]] [[W and Z bosons]] of the [[weak force]]. The remaining electrically neutral component separately couples to other particles known as [[fermion]]s (via [[Yukawa coupling]]s), causing these to [[mass generation|acquire mass]] as well. Some versions of the theory predict more than one kind of Higgs fields and bosons. Alternative [[Higgsless model|"Higgsless" models]] would have been considered if the Higgs boson were not discovered.
 
== A non-technical summary ==
{{Standard model of particle physics}}
 
=== "Higgs" terminology ===
:{| class="wikitable collapsible" style="fnt-size:90%"
|-
! colspan="2" | A simple explanation – what are the Higgs mechanism, field and boson?
|-
| ''[[Symmetry (physics)|Symmetries]] and [[force]]s''
| In the [[Standard Model|Standard Model of particle physics]], the [[fundamental force|fundamental forces of nature]] known to science arise from laws of nature called [[symmetry (physics)|symmetries]], and are [[force carrier|transmitted by particles]] known as [[gauge boson]]s. The [[weak force]]'s symmetry should cause its gauge bosons to have zero mass, but experiments show that the weak force's gauge bosons are actually very massive and short-ranging (now called [[W and Z bosons]]).{{#tag:ref |The range of a force is inversely proportional to the mass of the particles transmitting it.<ref>
{{cite book
|last=Shu |first=F. H.
|year=1982
|title=The Physical Universe: An Introduction to Astronomy
|url=http://books.google.com/books?id=v_6PbAfapSAC&pg=PA107
|pages=107–108
|publisher=[[University Science Books]]
|isbn=978-0-935702-05-7
}}</ref> In the Standard Model, forces are carried by [[virtual particles]]. These particles' movement and interactions with each other are limited by the [[uncertainty principle|energy–time uncertainty principle]]. As a result, the more massive a single virtual particle is, the greater its energy, and therefore the shorter the distance it can travel. A particle's mass therefore determines the maximum distance at which it can interact with other particles and on any force it mediates. By the same token, the reverse is also true: massless and near-massless particles can carry long distance forces. ''(See also: [[Compton wavelength]] and [[Static forces and virtual-particle exchange]])'' Since experiments have shown that the weak force acts over only a very short range, this implies that there must exist massive gauge bosons. And indeed, their masses have since been confirmed by measurement.|group="Note" |name="massvsrange"}} Their very short range – a result of their mass – makes structures like [[atom]]s and [[star]]s possible{{citation needed|reason=this is quite a big claim|date=October 2013}}, but it proved exceedingly difficult to find any way to explain their unexpected mass.
|-
| ''[[Higgs mechanism]]''
| By the early 1960s, physicists had realized that [[spontaneous symmetry breaking|a given symmetry law might not always be followed]] (or 'obeyed') under certain conditions.<ref group="Note">It is quite common for a law of physics to hold true only if certain assumptions held true or only under certain conditions. For example, [[Newton's laws of motion]] apply only at speeds where [[special relativity|relativistic effects]] are negligible; and laws related to conductivity, gases, and classical physics (as opposed to quantum mechanics) may apply only within certain ranges of size, temperature, pressure, or other conditions.</ref> The Higgs mechanism is a [[mathematical model|mathematical]] [[scientific model|model]] [[1964 PRL symmetry breaking papers|devised by three groups of researchers in 1964]] that explains why and how gauge bosons could still be massive despite their governing symmetry. It showed that the conditions for the symmetry would be 'broken' if an unusual type of [[field (physics)|field]] happened to exist throughout space, and then the particles would be able to have mass.
|-
| ''Higgs field''
| According to the Standard Model, a [[field (physics)|field]] of the necessary kind (the "Higgs field") exists throughout space, and breaks certain symmetry laws of the [[electroweak interaction]].<ref group="Note">Electroweak symmetry is broken by the Higgs field in its lowest energy state, called its "[[ground state]]". At high energy levels this does not happen, and the gauge bosons of the weak force would therefore be expected to be massless.</ref> The existence of this field triggers the Higgs mechanism, causing the gauge bosons responsible for the weak force to be massive, and explaining their very short range.<ref group="Note" name="massvsrange"/>
 
Some years after the original theory was articulated scientists realised that the same field would also explain, in a different way, why other fundamental constituents of matter (including [[electron]]s and [[quark]]s) have mass.
 
For many years scientists had no way to tell whether or not a field of this kind actually existed in reality. If it existed, it would be unlike any other fundamental field known in science. But it was also possible that these key ideas, or even the entire Standard Model itself, were somehow incorrect.<ref group="Note">By the 1960s, many had already started to see gauge theories as failing to explain particle physics because theorists had been unable to solve the mass problem or even explain how gauge theory could provide a solution. So the idea that the Standard Model – which relied on a "Higgs field" not yet proved to exist – could be fundamentally incorrect was far from fanciful. Against this, once the entire model was developed around 1972, no better theory yet existed, and its predictions and solutions were so accurate, that it became the preferred theory anyway. It then became crucial to science, to know whether it was ''correct''.</ref> Only discovering what was breaking this symmetry, would solve the problem.
|-
| ''Higgs boson''
| The existence of the Higgs field – the crucial question<ref name="OnyisiFAQ" /><ref name="strasslerFAQ2" /> – could be proven by [[Search for the Higgs boson|searching for]] a matching [[subatomic particle|particle]] associated with it, which would also have to exist—the "Higgs boson". Detecting Higgs bosons would automatically prove that the Higgs field exists, which would show the Standard Model is essentially correct. But for decades scientists had no way to discover whether Higgs bosons actually existed in nature either, because they would be very difficult to produce, and would [[particle decay|break apart]] in about a [[Names of small numbers|ten-sextillionth]] {{nowrap|([[Orders of magnitude (numbers)|10<sup>−22</sup>]])}} of a second. Although the theory gave "remarkably"&nbsp;<ref name="L&T"/>{{rp|22}}<ref name="predictions" group="Note" /> correct answers, [[particle collider]]s, detectors, and computers capable of looking for Higgs bosons took over 30 years {{nowrap|(c. 1980 – 2010)}} to develop.
 
As of 2013, scientists are virtually certain that they have proved the Higgs boson exists, and therefore that the concept of some type of Higgs field throughout space is proven. Further testing over the coming years should eventually tell us more about these, and is likely to have [[#Significance|significant impact]] in the future ''(see below)''.<ref name="dieter July 2012" /><ref name="CERN Nov 2012" />
|-
|}
 
=== Overview ===
In [[particle physics]], [[elementary particle]]s and forces give rise to the world around us. Nowadays, physicists explain the behaviour of these particles and how they interact using the [[Standard Model]]—a widely accepted and "remarkably" accurate<ref name="L&T"/> framework based on [[gauge invariance]]  and [[Symmetry (physics)|symmetries]], believed to explain almost everything in the world we see, other than [[gravity]].<ref>Heath, Nick, [http://www.techrepublic.com/blog/european-technology/the-cern-tech-that-helped-track-down-the-god-particle/815?tag=nl.e101/ ''The Cern tech that helped track down the God particle''], TechRepublic, 4 July 2012</ref>
 
But by around 1960 all attempts to create a gauge invariant theory for two of the four [[fundamental forces]] had consistently failed at one crucial point: although gauge invariance seemed extremely important, it seemed to make any theory of [[electromagnetism]] and the [[weak force]] go haywire, by demanding that either many particles with [[mass]] were massless or that non-existent forces and massless particles had to exist. Scientists had no idea how to get past this point.
 
Work done on [[superconductivity]] and [[spontaneous symmetry breaking|"broken" symmetries]] around 1960 led physicist [[Philip Warren Anderson|Philip Anderson]] to suggest in 1962 a new kind of solution that might hold the key. [[1964 PRL symmetry breaking papers|In 1964 a theory was created by 3 different groups of researchers]], that showed the problems could be resolved if an unusual kind of [[field (physics)|field]] existed throughout the universe. It would cause existing particles to [[mass generation|acquire mass]] instead of new massless particles being formed. By 1972 it had been developed into a comprehensive theory and proved capable of giving [[renormalization|"sensible" results]]. Although there was not yet any proof of such a field, calculations consistently gave answers and predictions that were confirmed by experiments, including very accurate [[Standard Model#Tests and predictions|predictions of several other particles]],<ref name="predictions" group="Note">The success of the Higgs based electroweak theory and Standard Model is illustrated by their [[Standard Model#Tests and predictions|predictions]] of the mass of two particles later detected: the W boson (predicted mass: 80.390 ± 0.018 GeV, experimental measurement: 80.387 ± 0.019 GeV), and the Z boson (predicted mass: 91.1874 ± 0.0021, experimental measurement: 91.1876 ± 0.0021 GeV). The existence of the Z boson was itself another prediction. Other correct predictions included the [[weak neutral current]], the [[gluon]], and the [[top quark|top]] and [[charm quark]]s, all later proven to exist as the theory said.</ref> so scientists began to believe this might be true and to search for proof whether or not a Higgs field exists in nature.
 
If this field did exist, this would be a monumental discovery for science and human knowledge, and is expected to open doorways to new knowledge in many fields. If not, then other more complicated theories would need to be explored. The easiest proof whether or not the field existed was by searching for a new kind of [[elementary particle|particle]] it would have to give off, known as "Higgs bosons" or the "Higgs particle". These would be extremely difficult to find, so it was only many years later that experimental technology became sophisticated enough to answer the question.
 
While several symmetries in nature are spontaneously broken through a form of the Higgs mechanism, in the context of the Standard Model the term "Higgs mechanism" almost always means symmetry breaking of the [[electroweak interaction|electroweak field]]. It is considered proven, but the exact cause has been [[Unanswered questions in physics|exceedingly difficult to prove]]. After 50 years, the Higgs boson's existence – apparently proven in 2013 – would finally confirm that the Standard Model is essentially correct and allow further development, while its non-existence would mean that other theories are needed instead.
 
[[#Media explanations and analogies|Various analogies]] have also been invented to describe the Higgs field and boson, including analogies with well-known symmetry breaking effects such as the [[rainbow]] and [[dispersive prism|prism]], [[electric field]]s, ripples, and resistance of macro objects moving through media, like people moving through crowds or some objects moving through [[syrup]] or [[molasses]]. However, analogies based on simple resistance to motion are inaccurate as the Higgs field does not work by resisting motion.
 
== Significance ==
 
=== Scientific impact ===
Evidence of the Higgs field and its properties would be extremely significant scientifically, for many reasons. The Higgs boson's importance is largely that it is able to be examined using existing knowledge and experimental technology, as a way to confirm and study the entire Higgs field theory.<ref name="OnyisiFAQ" /><ref name="strasslerFAQ2" /> Conversely, proof that the Higgs field and boson <u>do not</u> exist would also be significant. In discussion form, the relevance includes:
 
{| class="wikitable" style="font-size:90%; margin-left: 20px"
|-
| Validating the [[Standard Model]], or choosing between extensions and alternatives
| Does the Higgs field exist, which fundamentally validates the Standard Model? If it does, then which more advanced extensions are suggested or excluded based upon measurements of its properties? What else can we learn about this fundamental field, now that we have the experimental means to study its behavior and interactions?  Alternatively, if the Higgs field doesn't exist, which alternatives and modifications to the Standard Model are likely to be preferred? Will the data suggest an extension, or a completely different approach (such as [[supersymmetry]] or [[string theory]])?
 
Related to this, a belief generally exists among physicists that there is likely to be "new" [[physics beyond the Standard Model]]—the Standard Model will at some point be extended or superseded. The Higgs field and related issues present a promising "doorway" to understand better the places where the Standard Model might become inadequate or fail, and could provide considerable evidence guiding researchers into future enhancements or successors.
|-
| Finding how [[electroweak symmetry breaking|symmetry breaking]] happens within the [[electroweak interaction]]
| Below an extremely high temperature, [[electroweak symmetry breaking]] causes the [[electroweak interaction]] to manifest in part as the short-ranged [[weak force]], which is carried by massive [[gauge boson]]s. Without this, the universe we see around us could not exist, because [[atom]]s and other structures could not form, and reactions in stars such as our [[Sun]] would not occur. But it is not clear how this actually happens in nature. Is the Standard Model correct in its approach, and can it be made more exact with actual experimental measurements? If not the Higgs field, then what is breaking symmetry in its place?
|-
| Finding how certain particles [[mass generation|acquire mass]]
| Electroweak symmetry breaking (due to a Higgs field or otherwise) is believed proven responsible for the masses of fundamental particles such as elementary [[fermion]]s (including [[electron]]s and [[quark]]s) and the massive [[W and Z bosons|W and Z]] [[gauge boson]]s. Finding how this happens is pivotal to particle physics.
 
It is worth noting  that the Higgs field does not 'create' mass [[creatio ex nihilo|out of nothing]] (which would violate the [[law of conservation of energy]]). Nor is the Higgs field responsible for the mass of all particles. For example, about 99% of the mass of [[baryon]]s (composite particles such as the [[proton]] and [[neutron]]) is due instead to the [[kinetic energy]] of quarks and to the energies of (massless) [[gluon]]s of the [[strong interaction]] inside the baryons.<ref>{{cite web
|first=Achintya |last=Rao
|url=http://cms.web.cern.ch/news/why-would-i-care-about-higgs-boson CMS Public
|title=Why would I care about the Higgs boson?
|work=CMS Public Website
|publisher=CERN
|date=2 July 2012
|accessdate=18 July 2012
}}</ref> In Higgs-based theories, the property of 'mass' is a manifestation of [[potential energy]] transferred to particles when they interact ("couple") with the Higgs field, which had contained that mass [[mass–energy equivalence|in the form of energy]].<ref>Max Jammer, ''Concepts of Mass in Contemporary Physics and Philosophy'' (Princeton, NJ: Princeton University Press, 2000) pp.162–163, who provides many references in support of this statement.</ref>
|-
| Evidence whether or not [[scalar fields]] exist in nature, and [[physics beyond the Standard Model|"new" physics]]
| Proof of a [[scalar field]] such as the Higgs field would be hard to overestimate: ''"[The] verification of real scalar fields would be nearly as important as its role in generating mass".''&nbsp;<ref name="ScienceNews" />  [[Rolf-Dieter Heuer]], director general of CERN, stated in a 2011 talk on the Higgs field:<ref name="Heuer 2011">[http://cas.web.cern.ch/cas/Greece-2011/Lectures/heuer-chios-public-2011.pptx The Large Hadron Collider: Shedding Light on the Early Universe] – lecture by R.-D. Heuer, CERN, Chios, Greece, 28 September 2011</ref>
: "All the matter particles are spin-1/2 [[fermion]]s. All the force carriers are spin-1 bosons. Higgs particles are spin-0 bosons (scalars). The Higgs is neither matter nor force. The Higgs is just different. This would be the first fundamental scalar ever discovered. The Higgs field is thought to fill the entire universe. Could it give some handle of [[dark energy]] (scalar field)? Many modern theories predict other scalar particles like the Higgs. Why, after all, should the Higgs be the only one of its kind? [The] LHC can search for and study new scalars with precision."
|-
| Insight into [[cosmic inflation]]
| There has been considerable scientific research on possible links between the Higgs field and the [[inflaton]] – a hypothetical field suggested as the explanation for the [[metric expansion of space|expansion of space]] during [[Chronology of the universe|the first fraction of a second]] of the [[universe]] (known as the "[[inflationary epoch]]"). Some theories suggest that a fundamental scalar field might be responsible for this phenomenon; the Higgs field is such a field and therefore has led to papers analysing whether it could also be the ''inflaton'' responsible for this [[exponential growth|exponential]] expansion of the universe during the [[Big Bang]]. Such theories are highly tentative and face significant problems related to [[Unitarity (physics)|unitarity]], but may be viable if combined with additional features such as large non-minimal coupling, a [[Brans–Dicke theory|Brans–Dicke]] scalar, or other "new" physics, and have received treatments suggesting that Higgs inflation models are still of interest theoretically.
|-
| Insight into the nature of the [[universe]], and its [[fate of the universe|possible fates]]
|
{|  style="float:right; border:solid 1px darkgrey;"
|-
| [[File:Higgs-Mass-MetaStability.svg|frameless|border|200px|right]]
| style="width:200px;"| <span style="font-size:90%">Diagram showing the Higgs boson and [[top quark]] masses, which could indicate whether our universe is stable, or a [[metastability|long-lived 'bubble']].  As of 2012, the 2σ ellipse based on [[Tevatron]] and LHC data still allows for both possibilities.<ref name="Alekhin 2012"/></span>
|}
For decades, scientific models of our universe have included the possibility that it exists as a [[metastability|long-lived, but not completely stable]], sector of space, which could potentially at some time be destroyed upon '[[vacuum instability|toppling]]' into a [[false vacuum|more stable vacuum state]].<ref name="turnerwilczek">{{cite journal| author=M.S. Turner, F. Wilczek| title=Is our vacuum metastable? | journal=Nature |volume=298| year=1982| issue=5875 | pages= 633–634| doi=10.1038/298633a0|bibcode = 1982Natur.298..633T| ref=harv }}</ref><ref name="colemandeluccia">{{cite journal | author=S. Coleman and F. De Luccia| title=Gravitational effects on and of vacuum decay | journal=Physical Review | year=1980 | volume=D21 | page= 3305 | doi=10.1103/PhysRevD.21.3305 |bibcode = 1980PhRvD..21.3305C | issue=12 | ref=harv }}</ref><ref>{{cite journal | author = M. Stone | title =  Lifetime and decay of excited vacuum states | journal=Phys. Rev. D  | volume = 14  | year = 1976 | issue = 12 | pages = 3568–3573 | doi = 10.1103/PhysRevD.14.3568 |bibcode = 1976PhRvD..14.3568S | ref = harv }}</ref><ref>{{cite journal | author = P.H. Frampton | title = Vacuum Instability and Higgs Scalar Mass | journal=Phys. Rev. Lett. | volume = 37 | year = 1976 | issue = 21 | pages = 1378–1380 | doi = 10.1103/PhysRevLett.37.1378 | bibcode=1976PhRvL..37.1378F | ref = harv}}</ref><ref>{{cite journal | author = P.H. Frampton | title = Consequences of Vacuum Instability in Quantum Field Theory | journal = Phys. Rev. | volume = D15 | issue = 10 | year = 1977 | pages = 2922–28 | doi = 10.1103/PhysRevD.15.2922 | bibcode = 1977PhRvD..15.2922F | ref = harv }}</ref> If the masses of the Higgs boson and [[top quark]] are known more exactly, and the Standard Model provides a correct description of particle physics up to extreme energies of the [[Planck scale]], then it is possible to calculate whether the universe's present vacuum state is stable or merely long-lived.<ref>{{cite journal|last=Ellis, Espinosa, Giudice, Hoecker, & Riotto|title=The Probable Fate of the Standard Model|journal=Phys. Lett. B | volume = 679 | pages = 369–375 | year = 2009 | doi=10.1016/j.physletb.2009.07.054 | arxiv=0906.0954 | first1=J. | last2=Espinosa | first2=J.R. | last3=Giudice | first3=G.F. | last4=Hoecker | first4=A.|last5=Riotto|first5=A.|issue=4|ref=harv|bibcode = 2009PhLB..679..369E }}</ref><ref>{{cite journal|last=Masina|first=Isabella|title=Higgs boson and top quark masses as tests of electroweak vacuum stability|journal=Phys. Rev. D|date=2013-02-12|url=http://prd.aps.org/accepted/c0076Qe3K321150399409e37404f8f94e022e5321|ref=harv|bibcode=2013PhRvD..87e3001M|volume=87|page=53001|doi=10.1103/PhysRevD.87.053001|issue=5|arxiv = 1209.0393 }}</ref> (This was sometimes misreported as the Higgs boson "ending" the universe{{#tag:ref| For example, [[Huffington Post]]/[[Reuters]]<ref>{{cite news|last=Irene Klotz (editing by David Adams and Todd Eastham)|title=Universe Has Finite Lifespan, Higgs Boson Calculations Suggest|url=http://www.huffingtonpost.com/2013/02/19/universe-lifespan-finite-unstable-higgs-boson_n_2713053.html|accessdate=21 February 2013|newspaper=Huffington Post|date=2013-02-18|agency=Reuters|quote=Earth will likely be long gone before any Higgs boson particles set off an apocalyptic assault on the universe}}</ref> and others<ref>{{cite news|last=Hoffman|first=Mark|title=Higgs Boson Will Destroy The Universe Eventually|url=http://www.scienceworldreport.com/articles/5038/20130219/higgs-boson-instability-will-destroy-universe-eventually.htm|accessdate=21 February 2013|newspaper=ScienceWorldReport|date=2013-02-19}}</ref><ref>{{cite news|title=Higgs boson will aid in creation of the universe – and how it will end|url=http://www.catholic.org/technology/story.php?id=49808|accessdate=21 February 2013|newspaper=Catholic Online/NEWS CONSORTIUM|date=2013-02-20|quote=[T]he Earth will likely be long gone before any Higgs boson particles set off an apocalyptic assault on the universe}}</ref>}}). A {{nowrap|125 – 127 GeV}} Higgs mass seems to be extremely close to the boundary for stability (estimated in 2012 as {{nowrap|123.8 – 135.0 GeV}}<ref name="Alekhin 2012">{{cite journal|last=Alekhin, Djouadi and Moch|title=The top quark and Higgs boson masses and the stability of the electroweak vacuum|journal=Physics Letters B|date=2012-08-13|url=http://pubdb.desy.de/fulltext/getfulltext.php?uid=23383-59716|accessdate=20 February 2013|ref=harv|bibcode=2012PhLB..716..214A|last2=Djouadi|first2=A.|last3=Moch|first3=S.|volume=716|page=214|doi=10.1016/j.physletb.2012.08.024|first1=S.|arxiv = 1207.0980 }}</ref>) but a definitive answer requires much more precise measurements of the top quark's [[pole mass]].<ref name="Alekhin 2012" />
 
If measurements of the Higgs boson suggest that our universe lies within a [[false vacuum]] of this kind, then it would imply – more than likely in many billions of years<ref name="Boyle">{{cite news|last=Boyle|first=Alan|title=Will our universe end in a 'big slurp'? Higgs-like particle suggests it might|url=http://cosmiclog.nbcnews.com/_news/2013/02/18/17006552-will-our-universe-end-in-a-big-slurp-higgs-like-particle-suggests-it-might?lite|accessdate=21 February 2013|newspaper=NBC News' Cosmic log|date=2013-02-19|quote=[T]he bad news is that its mass suggests the universe will end in a fast-spreading bubble of doom. The good news? It'll probably be tens of billions of years}}. The article quotes [[Fermilab]]'s Joseph Lykken: "[T]he parameters for our universe, including the Higgs [and top quark's masses] suggest that we're just at the edge of stability, in a "metastable" state. Physicists have been contemplating such a possibility for more than 30 years. Back in 1982, physicists Michael Turner and Frank Wilczek wrote in Nature that "without warning, a bubble of true vacuum could nucleate somewhere in the universe and move outwards..."</ref>{{#tag:ref|The bubble's effects would be expected to propagate across the universe at the speed of light from wherever it occurred. However space is vast – with even [[Andromeda galaxy|the nearest galaxy]] being over 2 million [[lightyears]] from us, and others being many billions of lightyears distant, so the effect of such an event would be unlikely to arise here for billions of years after first occurring.<ref name="Boyle" /><ref>{{cite news|last=Peralta|first=Eyder|title=If Higgs Boson Calculations Are Right, A Catastrophic 'Bubble' Could End Universe|url=http://www.npr.org/blogs/thetwo-way/2013/02/19/172422921/if-higgs-boson-calculations-are-right-a-catastrophic-bubble-could-end-universe|accessdate=21 February 2013|newspaper=npr – two way|date=2013-02-19}} Article cites [[Fermilab]]'s Joseph Lykken: "The bubble forms through an unlikely quantum fluctuation, at a random time and place," Lykken tells us. "So in principle it could happen tomorrow, but then most likely in a very distant galaxy, so we are still safe for billions of years before it gets to us."</ref>|group="Note"}} – that the universe's forces, particles, and structures could cease to exist as we know them (and be replaced by different ones), if a true vacuum happened to [[nucleate]].<ref name="Boyle" /><ref group="Note">If the Standard Model is correct, then the particles and forces we observe in our universe exist as they do, because of underlying quantum fields. Quantum fields can have states of differing stability, including 'stable', 'unstable' and '[[metastability|metastable]]' states (the latter remain stable unless sufficiently [[Perturbation theory (quantum mechanics)|perturbed]]). If a more stable vacuum state were able to arise, then existing particles and forces would no longer arise as they presently do. Different particles or forces would arise from (and be shaped by) whatever new quantum states arose. The world we know depends upon these particles and forces, so if this happened, everything around us, from [[subatomic particle]]s to [[galaxy|galaxies]], and all [[fundamental force]]s, would be reconstituted into new fundamental particles and forces and structures. The universe would potentially lose all of its present structures and become inhabited by new ones (depending upon the exact states involved) based upon the same quantum fields.</ref> It also suggests that the Higgs [[self-coupling]] λ and its β<sub>λ</sub> function could be very close to zero at the Planck scale, with "intriguing" implications, including theories of gravity and Higgs-based inflation.<ref name="Alekhin 2012" />{{rp|218}} A future electron–positron collider would be able to provide the precise measurements of the top quark needed for such calculations.<ref name="Alekhin 2012" />
|-
| Insight into the [[vacuum energy|'energy of the vacuum']]
| More speculatively, the Higgs field has also been proposed as the [[Vacuum energy|energy of the vacuum]], which at the extreme energies of the first moments of the [[Big Bang]] caused the universe to be a kind of featureless symmetry of undifferentiated extremely high energy. In this kind of speculation, the single unified field of a [[Grand Unified Theory]] is identified as (or modeled upon) the Higgs field, and it is through successive symmetry breakings of the Higgs field or some similar field at [[phase transition]]s that the present universe's known forces and fields arise.<ref>{{cite news|last=Cole|first=K.|title=One Thing Is Perfectly Clear: Nothingness Is Perfect|url=http://articles.latimes.com/2000/dec/14/local/me-65457|accessdate=17 January 2013|newspaper=[[Los Angeles Times]]|date=2000-12-14|page='Science File'|quote=[T]he Higgs' influence (or the influence of something like it) could reach much further. For example, something like the Higgs—if not exactly the Higgs itself—may be behind many other unexplained "broken symmetries" in the universe as well ... In fact, something very much like the Higgs may have been behind the collapse of the symmetry that led to the Big Bang, which created the universe. When the forces first began to separate from their primordial sameness—taking on the distinct characters they have today—they released energy in the same way as water releases energy when it turns to ice. Except in this case, the freezing packed enough energy to blow up the universe. ... However it happened, the moral is clear: Only when the perfection shatters can everything else be born.}}</ref>
|-
| Link to the [[cosmological constant|'cosmological constant' problem]]
| The relationship (if any) between the Higgs field and the presently observed [[Vacuum energy|vacuum energy density]] of the universe has also come under scientific study. As observed, the present vacuum energy density is extremely close to zero, but the energy density expected from the Higgs field, supersymmetry, and other current theories are typically many orders of magnitude larger. It is unclear how these should be reconciled. This [[cosmological constant|cosmological constant problem]] remains a further major [[unanswered questions in physics|unanswered problem]] in physics.
{{further|Zero-point energy|Vacuum state}}
|}
 
==="Real world" impact===
As yet, there are no known immediate technological benefits of finding the Higgs particle. However, observers in both media and science point out that when fundamental discoveries are made about our world, their practical uses can take decades to emerge, but are often world-changing when they do.<ref name="NYT practical">[http://www.nytimes.com/2012/11/30/opinion/global/kathy-sykes-higgs-matters.html Higgs Matters] – Kathy Sykes, 30 Nove 2012</ref><ref name="APS practical">[http://www.aps.org/publications/capitolhillquarterly/201207/higgsbosom.cfm Why the public should care about the Higgs Boson] – Jodi Lieberman, [[American Physical Society]] (APS)</ref><ref name="strassler practical">[http://profmattstrassler.com/articles-and-posts/the-higgs-particle/why-the-higgs-particle-matters Matt Strassler's blog – Why the Higgs particle matters] 2 July 2012</ref> A common pattern for fundamental discoveries is for practical applications to follow later, once the discovery has been explored further, at which point they become the basis for social change and new technologies.
 
For example, in the first half of the 20th century it was not expected that [[quantum mechanics]] would make possible [[transistor]]s and [[microchip]]s, [[mobile phone]]s and [[computer]]s, [[laser]]s and [[MRI scanner|M.R.I. scanners]].<ref name="nasa 2004">[http://science.nasa.gov/science-news/science-at-nasa/2004/26mar_einstein Evicting Einstein], March 26, 2004, [[NASA]]. ''"Both [relativity and quantum mechanics] are extremely successful. The Global Positioning System (GPS), for instance, wouldn't be possible without the theory of relativity. Computers, telecommunications, and the Internet, meanwhile, are spin-offs of quantum mechanics."''</ref> [[Radio waves]] were described by [[Heinrich Hertz|their co-discoverer]] in 1888 as "an interesting laboratory experiment" with "no useful purpose" whatsoever,<ref>[http://einstein.stanford.edu/content/faqs/4forces.html Examples of Great Discoveries in the Fundamental Forces] – Gravity probe B [[FAQ]], [[Stanford University]] website, 2012</ref> and are now used in innumerable ways ([[radar]], [[weather prediction]], [[electrocoagulation|medicine]], [[television]], [[wireless computing]] and [[emergency services|emergency response]]), [[positron]]s are used in hospital [[tomography]] scans, and [[special relativity|special]] and [[general relativity]] which explain [[black hole]]s also enable [[satellite]]-based [[Global Positioning System|GPS]] and [[satellite navigation]] ("satnav").<ref name="nasa 2004" /> [[Electric power]] [[power generation|generation]] and [[power transmission|transmission]], [[electric motor|motors]], and [[lighting]], all stemmed from previous theoretical work on [[electricity]] and [[magnetism]]; [[air conditioning]] and [[refrigeration]] resulted from [[thermodynamics]]. It is impossible to predict how seemingly esoteric knowledge may affect society in the future.<ref name="NYT practical" /><ref name="strassler practical" />
 
Other observers highlight technological spin-offs from this and related particle physics activities, which have already brought major developments to society. For example, the [[World Wide Web]] as used today<!--WORDING IMPORTANT HERE, OTHER PREVIOUS NETWORKS EXISTED THAT MAY BE CONFUSED WITH THE WWW--> was created by physicists working in global collaborations on particle experiments at CERN to share their results, and the results of massive amounts of data produced by the Large Hadron Collider have already led to significant advances in [[distributed computing|distributed]] and [[cloud computing]], now well established within mainstream services.<ref name="APS practical" />
 
== History ==
{{See also|1964 PRL symmetry breaking papers|Higgs mechanism}}
{| class="wikitable" style="float:right; margin:0 0 1em 1em; font-size:85%; width:354px;"
|-
| {{nowrap|[[File:AIP-Sakurai-best.JPG|x150px]]&nbsp;&nbsp;[[File:Higgs, Peter (1929) cropped.jpg|x150px]]}}<br />
The six authors of the [[1964 PRL symmetry breaking papers|1964 PRL papers]], who received the 2010 [[Sakurai Prize|J. J. Sakurai Prize]] for their work. From left to right: [[T. W. B. Kibble|Kibble]], [[Gerald Guralnik|Guralnik]], [[C. R. Hagen|Hagen]], [[François Englert|Englert]], [[Robert Brout|Brout]]. ''Right:'' [[Peter Higgs|Higgs]].
|}
 
Particle physicists study [[matter]] made from [[fundamental particle]]s whose interactions are mediated by exchange particles - [[gauge boson]]s - acting as [[force carrier]]s. At the beginning of the 1960s a number of these particles had been discovered or proposed, along with theories suggesting how they relate to each other, some of which had already been reformulated as [[quantum field theory|field theories]] in which the objects of study are not particles and forces, but [[quantum field]]s and their [[Symmetry (physics)|symmetries]].<ref name="Carroll2012">{{cite book|author=Sean Carroll|title=The Particle at the End of the Universe: How the Hunt for the Higgs Boson Leads Us to the Edge of a New World|date=13 November 2012|publisher=Penguin Group US|isbn=978-1-101-60970-5}}</ref>{{rp|150}} However, [[Unified field theory|attempts to unify]] known [[fundamental forces]] such as the [[electromagnetic force]] and the [[weak nuclear force]] were known to be incomplete. One known omission was that [[gauge invariance|gauge invariant]] approaches, including [[non-abelian gauge theory|non-abelian]] models such as [[Yang–Mills theory]] (1954), which held great promise for unified theories, also seemed to predict known massive particles as massless.<ref name=woit>{{cite web|last=Woit|first=Peter|title=The Anderson–Higgs Mechanism|url=http://www.math.columbia.edu/~woit/wordpress/?p=3282|publisher=Dr. Peter Woit (Senior Lecturer in Mathematics [[Columbia University]] and Ph.D. particle physics)|accessdate=12 November 2012|date=13 November 2010}}</ref> [[Goldstone's theorem]], relating to [[continuous symmetry|continuous symmetries]] within some theories, also appeared to rule out many obvious solutions,<ref>{{cite journal | last =Goldstone | first = J | year = 1962 | title = Broken Symmetries | journal = Physical Review | volume = 127 | pages = 965–970 | doi =10.1103/PhysRev.127.965 | last2 =Salam | first2 =Abdus | last3 =Weinberg | first3 =Steven |bibcode = 1962PhRv..127..965G | issue =3 | ref =harv }}</ref> since it appeared to show that zero-mass particles would have to also exist that were "simply not seen".<ref name="Guralnik 2011">{{cite arXiv |last=Guralnik |first=G. S. |year=2011 |title=The Beginnings of Spontaneous Symmetry Breaking in Particle Physics |eprint=1110.2253 |class=physics.hist-ph}}</ref> According to [[Gerald Guralnik|Guralnik]], physicists had "no understanding" how these problems could be overcome.<ref name="Guralnik 2011" />
 
Particle physicist and mathematician Peter Woit summarised the state of research at the time:
 
: "Yang and Mills work on non-abelian gauge theory had one huge problem: in [[perturbation theory]] it has massless particles which don’t correspond to anything we see. One way of getting rid of this problem is now fairly well-understood, the phenomenon of [[color confinement|confinement]] realized in [[quantum chromodynamics|QCD]], where the strong interactions get rid of the massless “gluon” states at long distances. By the very early sixties, people had begun to understand another source of massless particles: spontaneous symmetry breaking of a continuous symmetry. What Philip Anderson realized and worked out in the summer of 1962 was that, when you have ''both'' gauge symmetry ''and'' spontaneous symmetry breaking, the Nambu–Goldstone massless mode can combine with the massless gauge field modes to produce a physical massive vector field. This is what happens in [[superconductivity]], a subject about which Anderson was (and is) one of the leading experts." ''[text condensed]'' <ref name="woit" />
 
The Higgs mechanism is a process by which [[vector boson]]s can get [[rest mass]] ''without'' [[explicit symmetry breaking|explicitly breaking]] [[gauge invariance]], as a byproduct of [[spontaneous symmetry breaking]].<ref name="scholarpedia">{{cite journal |last=Kibble |first=T. W. B.  |year=2009 |url=http://www.scholarpedia.org/article/Englert-Brout-Higgs-Guralnik-Hagen-Kibble_mechanism |title=Englert–Brout–Higgs–Guralnik–Hagen–Kibble Mechanism |work=[[Scholarpedia]] |volume=4 |issue=1 |pages=6441 |doi=10.4249/scholarpedia.6441 |accessdate=2012-11-23|bibcode = 2009SchpJ...4.6441K }}</ref><ref name="scholarpedia_a">{{cite journal |last=Kibble |first=T. W. B. |year= |url=http://www.scholarpedia.org/article/Englert-Brout-Higgs-Guralnik-Hagen-Kibble_mechanism_%28history%29 |title=History of Englert–Brout–Higgs–Guralnik–Hagen–Kibble Mechanism (history) |journal=[[Scholarpedia]] |volume=4 |issue=1 |page=8741 |doi=10.4249/scholarpedia.8741 |accessdate=2012-11-23|bibcode = 2009SchpJ...4.8741K }}</ref> The mathematical theory behind spontaneous symmetry breaking was initially conceived and published within particle physics by [[Yoichiro Nambu]] in 1960,<ref name="nambu nobel">[http://www.nobelprize.org/nobel_prizes/physics/laureates/2008 The Nobel Prize in Physics 2008] – official Nobel Prize website.</ref> the concept that such a mechanism could offer a possible solution for the "mass problem" was originally suggested in 1962 by [[Philip Warren Anderson|Philip Anderson]] (who had previously written papers on broken symmetry and its outcomes in superconductivity<ref>{{plain link|url=http://publish.aps.org/search?q=&clauses%5b%5d%5boperator%5d=AND&clauses%5b%5d%5bfield%5d=author&clauses%5b%5d%5bvalue%5d=anderson&clauses%5b%5d%5boperator%5d=AND&clauses%5b%5d%5bfield%5d=abstitle&clauses%5b%5d%5bvalue%5d=&clauses%5b%5d%5boperator%5d=AND&clauses%5b%5d%5bfield%5d=all&clauses%5b%5d%5bvalue%5d=symmetry&per_page=25|name=List of Anderson 1958–1959 papers referencing 'symmetry'}}, at APS Journals</ref> and concluded in his 1963 paper on Yang-Mills theory that ''"considering the superconducting analog... [t]hese two types of bosons seem capable of canceling each other out... leaving finite mass bosons"''),<ref name="MyLifeAsABoson">{{cite web|last=Higgs|first=Peter|title=My Life as a Boson|url=http://www.kcl.ac.uk/nms/depts/physics/news/events/MyLifeasaBoson.pdf|publisher=Talk given by Peter Higgs at Kings College, London, Nov 24 2010, expanding on a paper originally presented in 2001|accessdate=17 January 2013|date=2010-11-24}} – the original 2001 paper can be found at: {{cite book|title=2001 A Spacetime Odyssey: Proceedings of the Inaugural Conference of the Michigan Center for Theoretical Physics, Michigan, USA, 21–25 May 2001|year=conference 2001, book of proceedings 2003|isbn=9812382313|publisher=World Scientific|editor=Duff and Liu|url=http://books.google.com/?id=ONhnbpq00xIC&pg=PR11&dq=2001:+A+Space+Time+Odyssey++%22life+as+a+boson%22#v=onepage&q=2001%3A%20A%20Space%20Time%20Odyssey%20%20%22life%20as%20a%20boson%22&f=false|pages=86–88|accessdate=17 January 2013}}</ref>{{rp|4–5}}<ref name="Anderson 1963">{{cite journal|title=Plasmons, gauge invariance and mass|doi=10.1103/PhysRev.130.439|year=1963|last1=Anderson|first1=P.|journal=Physical Review|volume=130|page=439|bibcode=1963PhRv..130..439A|ref=harv}}</ref> and [[Abraham Klein (physicist)|Abraham Klein]] and [[Benjamin W. Lee|Benjamin Lee]] showed in March 1964 that Goldstone's theorem could be avoided this way in at least some non-relativistic cases and speculated it might be possible in truly relativistic cases.<ref>{{Cite journal
| last1 = Klein | first1 = A.
| last2 = Lee | first2 = B.
| doi = 10.1103/PhysRevLett.12.266
| title = Does Spontaneous Breakdown of Symmetry Imply Zero-Mass Particles?
| journal = Physical Review Letters
| volume = 12
| issue = 10
| page = 266
| year = 1964
| pmid = 
| pmc =
|bibcode = 1964PhRvL..12..266K }}</ref>
 
These approaches were quickly developed into a full [[Special relativity|relativistic]] model, independently and almost simultaneously, by three groups of physicists: by [[François Englert]] and [[Robert Brout]] in August 1964;<ref name="eb64">{{Cite journal
|last=Englert |first=François |authorlink=François Englert
|last2=Brout |first2=Robert |authorlink2=Robert Brout
|year=1964
|title=Broken Symmetry and the Mass of Gauge Vector Mesons
|journal=[[Physical Review Letters]]
|volume=13 |issue=9 |pages=321–23
|doi=10.1103/PhysRevLett.13.321 |bibcode=1964PhRvL..13..321E
|ref=harv
}}</ref> by [[Peter Higgs]] in October 1964;<ref name="higgs64">{{Cite journal
|first=Peter |last=Higgs
|year=1964
|title=Broken Symmetries and the Masses of Gauge Bosons
|journal=[[Physical Review Letters]]
|volume=13 |issue=16 |pages=508–509
|doi=10.1103/PhysRevLett.13.508
|bibcode=1964PhRvL..13..508H
|ref=harv
}}</ref> and by [[Gerald Guralnik]], [[C. R. Hagen|Carl Hagen]], and [[T. W. B. Kibble|Tom Kibble]] (GHK) in November 1964.<ref name="ghk64">{{Cite journal
|last=Guralnik |first=Gerald |authorlink=Gerald Guralnik
|last2=Hagen |first2=C. R. |authorlink2=C. R. Hagen
|last3=Kibble |first3=T. W. B. |authorlink3=T. W. B. Kibble
|year=1964
|title=Global Conservation Laws and Massless Particles
|journal=[[Physical Review Letters]]
|volume=13 |issue=20 |pages=585–587
|doi=10.1103/PhysRevLett.13.585 |bibcode=1964PhRvL..13..585G
|ref=harv
}}</ref> Higgs also wrote a short but important<ref name="scholarpedia"/> response published in September 1964 to an objection by [[Walter Gilbert|Gilbert]],<ref name="higgs64note">{{Cite journal
|first=Peter |last=Higgs
|year=1964
|title=Broken symmetries, massless particles and gauge fields
|journal=[[Physics Letters]]
|volume=12 |issue=2 |pages=132–133
|doi=10.1016/0031-9163(64)91136-9
|ref=harv
|bibcode = 1964PhL....12..132H }}</ref> which showed that if calculating within the radiation gauge, Goldstone's theorem and Gilbert's objection would become inapplicable.<ref group="Note" name="GoldstoneNote" /> (Higgs later described Gilbert's objection as prompting his own paper.<ref>{{cite web|last=Higgs|first=Peter|title=My Life as a Boson|url=http://www.kcl.ac.uk/nms/depts/physics/news/events/MyLifeasaBoson.pdf|publisher=Talk given by Peter Higgs at Kings College, London, Nov 24 2010|accessdate=17 January 2013|date=2010-11-24|quote=Gilbert ... wrote a response to [Klein and Lee's paper] saying 'No, you cannot do that in a relativistic theory. You cannot have a preferred unit time-like vector like that.' This is where I came in, because the next month was when I responded to Gilbert’s paper by saying 'Yes, you can have such a thing' but only in a gauge theory with a gauge field coupled to the current.}}</ref>) Properties of the model were further considered by Guralnik in 1965,<ref>{{cite journal |author=G.S. Guralnik |year=2011 |title=Gauge invariance and the Goldstone theorem – 1965 Feldafing talk |journal=[[Modern Physics Letters A]] |volume=26 |issue=19 |pages=1381–1392 |doi=10.1142/S0217732311036188 |arxiv=1107.4592 |bibcode = 2011MPLA...26.1381G |ref=harv }}</ref> by Higgs in 1966,<ref>{{Cite journal|first=Peter |last=Higgs |year=1966 |title=Spontaneous Symmetry Breakdown without Massless Bosons |journal=[[Physical Review]] |volume=145 |issue=4 |pages=1156–1163 |doi=10.1103/PhysRev.145.1156 |bibcode = 1966PhRv..145.1156H|ref=harv }}</ref> by Kibble in 1967,<ref>{{Cite journal|first=Tom |last=Kibble |year=1967 |title=Symmetry Breaking in Non-Abelian Gauge Theories |journal=[[Physical Review]] |volume=155 |issue=5 |pages=1554–1561 |doi=10.1103/PhysRev.155.1554|ref=harv|bibcode = 1967PhRv..155.1554K }}</ref> and further by GHK in 1967.<ref>{{cite book |url=http://www.datafilehost.com/download-7d512618.html |last1=Guralnik |first1=G. S. |last2=Hagen |first2=C. R. |last3=Kibble |first3=T. W. B. |year=1967 |title=Broken Symmetries and the Goldstone Theorem |series=[[Advances in Physics]] |volume=2}}</ref> The original three 1964 papers showed that when a [[gauge theory]] is combined with an additional field that spontaneously breaks the symmetry, the gauge bosons can consistently acquire a finite mass.<ref name="scholarpedia" /><ref name="scholarpedia_a" /><ref name="prl">{{Cite journal
|url=http://prl.aps.org/50years/milestones#1964
|title=Physical Review Letters&nbsp;– 50th Anniversary Milestone Papers
|publisher=[[Physical Review Letters]]
|ref=harv
}}</ref> In 1967, [[Steven Weinberg]]<ref>
{{cite journal
| author=S. Weinberg
| year=1967
| title=A Model of Leptons
| journal=[[Physical Review Letters]]
| volume=19 | pages=1264–1266
| doi=10.1103/PhysRevLett.19.1264
| bibcode=1967PhRvL..19.1264W
| issue=21
| ref=harv
}}</ref> and [[Abdus Salam]]<ref>
{{cite conference
| author=A. Salam
| editor=N. Svartholm
| year=1968
| booktitle=Elementary Particle Physics: Relativistic Groups and Analyticity
| pages=367
| conference=Eighth Nobel Symposium
| publisher=Almquvist and Wiksell
| location=Stockholm
}}</ref> independently showed how a Higgs mechanism could be used to break the electroweak symmetry of [[Sheldon Lee Glashow|Sheldon Glashow]]'s [[electroweak theory|unified model for the weak and electromagnetic interactions]]<ref>
{{cite journal
| author=S.L. Glashow
| year=1961
| title=Partial-symmetries of weak interactions
| journal=[[Nuclear Physics (journal)|Nuclear Physics]]
| volume=22 | pages=579–588
| doi=10.1016/0029-5582(61)90469-2
|bibcode = 1961NucPh..22..579G
| issue=4
| ref=harv }}</ref> (itself an extension of work by [[Julian Schwinger|Schwinger]]), forming what became the [[Standard Model]] of particle physics. Weinberg was the first to observe that this would also provide mass terms for the fermions.<ref name="Ellis2012">{{cite arXiv
|title=A Historical Profile of the Higgs Boson
|first1=John |last1=Ellis
|first2=Mary K. |last2=Gaillard
|first3=Dimitri V. |last3=Nanopoulos
|eprint=1201.6045
|class=hep-ph
|year=2012}}</ref>&nbsp;{{#tag:ref|A field with the "Mexican hat" potential <math>V(\phi)= \mu^2\phi^2 + \lambda\phi^4</math> and <math>\mu^2 < 0</math> has a minimum not at zero but at some non-zero value <math>\phi_0</math>. By expressing the action in terms of the field <math>\tilde \phi = \phi-\phi_0</math> (where <math>\phi_0</math> is a constant independent of position), we find the Yukawa term has a component <math>g\phi_0 \bar\psi\psi</math>. Since both ''g'' and <math>\phi_0</math> are constants, this looks exactly like the mass term for a fermion of mass <math>g\phi_0</math>. The field <math>\tilde\phi</math> is then the [[Higgs field]].|group=Note}}
 
However, the seminal papers on spontaneous breaking of gauge symmetries were at first largely ignored, because it was widely believed that the (non-Abelian gauge) theories in question were a dead-end, and in particular that they could not be [[renormalizable|renormalised]]<!-- BRITISH ENGLISH SPELLING!-->. In 1971–72, [[Martinus Veltman]] and [[Gerard 't Hooft]] proved renormalisation of Yang–Mills was possible in two papers covering massless, and then massive, fields.<ref name="Ellis2012"/> Their contribution, and others' work on the [[renormalization group]] - including "substantial" theoretical work by [[physics in the USSR|Russian physicists]]<ref>{{cite web|url=http://www.nobelprize.org/nobel_prizes/physics/laureates/1999/veltman-lecture.pdf |title=Martin Veltman Nobel Lecture, December 12, 1999, p.391 |format=PDF |date= |accessdate=2013-10-09}}</ref> - was eventually "enormously profound and influential",<ref name="Politzer 2004">{{cite web|last=Politzer|first=David|title=The Dilemma of Attribution|url=http://www.nobelprize.org/nobel_prizes/physics/laureates/2004/politzer-lecture.html|work=Nobel Prize lecture, 2004|publisher=Nobel Prize|accessdate=22 January 2013|quote=Sidney Coleman published in Science magazine in 1979 a citation search he did documenting that essentially no one paid any attention to Weinberg’s Nobel Prize winning paper until the work of ’t Hooft (as explicated by Ben Lee). In 1971 interest in Weinberg’s paper exploded. I had a parallel personal experience: I took a one-year course on weak interactions from Shelly Glashow in 1970, and he never even mentioned the Weinberg–Salam model or his own contributions.}}</ref>  but even with all key elements of the eventual theory published there was still almost no wider interest. For example, [[Sidney Coleman|Coleman]] found in a study that "essentially no-one paid any attention" to Weinberg's paper prior to 1971{{#tag:ref| {{cite journal|last=[[Sidney Coleman{{!}}Coleman]]|first=Sidney|title=The 1979 Nobel Prize in Physics|journal=[[Science (magazine){{!}}Science]]|date=1979-12-14|volume=206|issue=4424|pages=1290–1292|doi=10.1126/science.206.4424.1290|url=http://www.sciencemag.org/content/206/4424/1290.extract|accessdate=22 January 2013|ref=harv|bibcode = 1979Sci...206.1290C }} – discussed by [[David Politzer]] in his 2004 Nobel speech.<ref name="Politzer 2004" />|name="Coleman 1979"}} – now the most cited in particle physics<ref name="PRL_50years">[http://prl.aps.org/50years/milestones#1967 Letters from the Past – A PRL Retrospective] (50 year celebration, 2008)</ref> – and even in 1970 according to [[David Politzer|Politzer]], Glashow's teaching of the weak interaction contained no mention of Weinberg's, Salam's, or Glashow's own work.<ref name="Politzer 2004" /> In practice, Politzer states, almost everyone learned of the theory due to physicist [[Benjamin W. Lee|Benjamin Lee]], who combined the work of Veltman and 't Hooft with insights by others, and popularised the completed theory.<ref name="Politzer 2004" /> In this way, from 1971, interest and acceptance "exploded"&nbsp;<ref name="Politzer 2004" /> and the ideas were quickly absorbed in the mainstream.<ref name="Ellis2012"/><ref name="Politzer 2004" />
 
The resulting electroweak theory and Standard Model have [[Standard Model#Tests and predictions|correctly predicted]] (among other discoveries) [[weak neutral current]]s, [[W and Z bosons|three bosons]], the [[top quark|top]] and [[charm quark]]s, and with great precision, the mass and other properties of some of these.<ref name="predictions" group="Note" />  Many of those involved [[#Recognition and awards|eventually won]] [[Nobel Prize]]s or other renowned awards. A 1974 paper and comprehensive review in ''[[Reviews of Modern Physics]]'' commented that "while no one doubted the [mathematical] correctness of these arguments, no one quite believed that nature was diabolically clever enough to take advantage of them",<ref name="Bernstein 1974">{{cite journal|last=[[Jeremy Bernstein]]|title=Spontaneous symmetry breaking, gauge theories, the Higgs mechanism and all that|journal=Reviews of Modern Physics|date=January 1974|volume=46 |issue=1 |page=7|url=http://www.calstatela.edu/faculty/kaniol/p544/rmp46_p7_higgs_goldstone.pdf|accessdate=2012-12-10|ref=harv|bibcode = 1974RvMP...46....7B |doi = 10.1103/RevModPhys.46.7 }}</ref>{{rp|9}} adding that the theory had so far produced meaningful answers that accorded with experiment, but it was unknown whether the theory was actually correct.<ref name="Bernstein 1974" />{{rp|9,36(footnote),43–44,47}} By 1986 and again in the 1990s it became possible to write that understanding and proving the Higgs sector of the Standard Model was "the central problem today in particle physics."&nbsp;<ref>{{cite book|last=José Luis Lucio and Arnulfo Zepeda|title=Proceedings of the II Mexican School of Particles and Fields, Cuernavaca-Morelos, 1986|year=1987|publisher=World Scientific|isbn=9971504340|page=29|url=http://books.google.com/?id=jJ-yAAAAIAAJ&q=higgs+%22central+problem+today+in+particle+physics%22&dq=higgs+%22central+problem+today+in+particle+physics%22}}</ref><ref>{{cite book|last=Gunion, Dawson, Kane, and Haber|title=The Higgs Hunter's Guide (1st ed.)|year=199|pages=11 (?)|url=http://books.google.com/?id=M5moXN_SA-MC&pg=PA10&dq=higgs+hunter+crucial+central+prediction#v=snippet&q=central&f=false|isbn=9780786743186}} – quoted as being in the first (1990) edition of the book by Peter Higgs in his talk "My Life as a Boson", 2001, ref#25.</ref>
 
=== Summary and impact of the PRL papers ===
{{Wikinewshas|news related to|
* [[n:2010 Sakurai Prize awarded for 1964 Higgs Boson theory work|2010 Sakurai Prize awarded for 1964 Higgs Boson theory work]]
* [[n:Prospective Nobel Prize for Higgs boson work disputed|Prospective Nobel Prize for Higgs boson work disputed (2010)]]
}}
The three papers written in 1964 were each recognised as milestone papers during ''[[Physical Review Letters]]''{{'s}} 50th anniversary celebration.<ref name="prl" /> Their six authors were also awarded the 2010 [[Sakurai Prize|J. J. Sakurai Prize for Theoretical Particle Physics]] for this work.<ref name="sakuraiprize">American Physical Society – {{cite web|url=http://www.aps.org/units/dpf/awards/sakurai.cfm|title=J. J. Sakurai Prize for Theoretical Particle Physics}}</ref> (A controversy also arose the same year, because in the event of a [[Nobel Prize]] only up to three scientists could be recognised, with six being credited for the papers.<ref>{{cite news|last=Merali|first=Zeeya|title=Physicists get political over Higgs|url=http://www.nature.com/news/2010/100804/full/news.2010.390.html|accessdate=28 December 2011|newspaper=[[Nature Magazine]]|date=4 August 2010}}</ref> ) Two of the three PRL papers (by Higgs and by GHK) contained equations for the hypothetical [[quantum field theory|field]] that eventually would become known as the Higgs field and its hypothetical [[quantum]], the Higgs boson.<ref name="higgs64" /><ref name="ghk64" /> Higgs' subsequent 1966 paper showed the decay mechanism of the boson; only a massive boson can decay and the decays can prove the mechanism.{{citation needed|date=August 2012}}
 
In the paper by Higgs the boson is massive, and in a closing sentence Higgs writes that "an essential feature" of the theory "is the prediction of incomplete multiplets of [[scalar boson|scalar]] and [[vector boson]]s".<ref name="higgs64"/> ([[Frank Close]] comments that 1960s gauge theorists were focused on the problem of massless ''vector'' bosons, and the implied existence of a massive ''scalar'' boson was not seen as important; only Higgs directly addressed it.<ref name="frank_close_infinity_puzzle" />{{rp|154, 166, 175}}) In the paper by GHK the boson is massless and decoupled from the massive states.<ref name="ghk64" /> In reviews dated 2009 and 2011, Guralnik states that in the GHK model the boson is massless only in a lowest-order approximation, but it is not subject to any constraint and acquires mass at higher orders, and adds that the GHK paper was the only one to show that there are no massless [[Goldstone boson]]s in the model and to give a complete analysis of the general Higgs mechanism.<ref name="Guralnik 2011"/><ref name="Guralnik 2009">{{Cite journal | author=G.S. Guralnik | title=The History of the Guralnik, Hagen and Kibble development of the Theory of Spontaneous Symmetry Breaking and Gauge Particles | journal=[[International Journal of Modern Physics A]] | year=2009 | volume=24 | issue=14 | pages=2601–2627 | doi=10.1142/S0217751X09045431 | arxiv=0907.3466|bibcode = 2009IJMPA..24.2601G | ref=harv }}</ref> All three reached similar conclusions, despite their very different approaches: Higgs' paper essentially used classical techniques, Englert and Brout's involved calculating vacuum polarization in perturbation theory around an assumed symmetry-breaking vacuum state, and GHK used operator formalism and conservation laws to explore in depth the ways in which Goldstone's theorem may be worked around.<ref name="scholarpedia" />
 
In addition to explaining how mass is acquired by vector bosons, the Higgs mechanism also predicts the ratio between the [[W and Z bosons|W boson and Z boson]] masses as well as their [[coupling constant|couplings]] with each other and with the Standard Model quarks and leptons.{{citation needed|date=August 2012}} Subsequently, many of these predictions have been verified by precise measurements performed at the [[Large Electron–Positron Collider|LEP]] and the [[Stanford Linear Collider|SLC]] colliders, thus overwhelmingly confirming that some kind of Higgs mechanism does take place in nature,<ref name="EWWG">{{cite web |url=http://lepewwg.web.cern.ch/LEPEWWG/ |title=LEP Electroweak Working Group}}</ref> but the exact manner by which it happens has not yet been discovered.{{citation needed|date=August 2012}} The results of searching for the Higgs boson are expected to provide evidence about how this is realized in nature.{{citation needed|date=August 2012}}
 
== Theoretical properties ==
{{main|Higgs mechanism}}
 
=== Theoretical need for the Higgs ===
[[File:Spontaneous symmetry breaking (explanatory diagram).png|thumb|right|250px|"[[Spontaneous symmetry breaking|Symmetry breaking]] illustrated": – At high energy levels ''(left)'' the ball settles in the center, and the result is symmetrical. At lower energy levels ''(right)'', the overall "rules" remain symmetrical, but the "Mexican hat" potential comes into effect: [[local property|"local" symmetry]] inevitably becomes broken since eventually the ball must at random roll one way or another.]]
[[Gauge invariance]] is an important property of modern particle theories such as the [[Standard Model]], partly due to its success in other areas of fundamental physics such as [[electromagnetism]] and the [[strong interaction]] ([[quantum chromodynamics]]). However, there were great difficulties in developing gauge theories for the [[weak nuclear force]] or a possible unified [[electroweak interaction]]. [[Fermion]]s with a mass term would violate gauge symmetry and therefore cannot be gauge invariant. (This can be seen by examining the [[Lagrangian#Lagrangians in quantum field theory|Dirac Lagrangian]] for a fermion in terms of left and right handed components; we find none of the spin-half particles could ever flip [[helicity (particle physics)|helicity]] as required for mass, so they must be massless.<ref group="Note">In the Standard Model, the mass term arising from the Dirac Lagrangian for any fermion <math>\psi</math> is <math>-m\bar{\psi}\psi</math>. This is ''not'' invariant under the electroweak symmetry, as can be seen by writing <math>\psi</math> in terms of left and right handed components:
:<math>-m\bar{\psi}\psi\;=\;-m(\bar{\psi}_L\psi_R+\bar{\psi}_R\psi_L)</math>
i.e., contributions from <math>\bar{\psi}_L\psi_L</math> and <math>\bar{\psi}_R\psi_R</math> terms do not appear. We see that the mass-generating interaction is achieved by constant flipping of particle [[chirality]]. Since the spin-half particles have no right/left helicity pair with the same [[SU(2)]] and [[SU(3)]] representation and the same weak hypercharge, then assuming these gauge charges are conserved in the vacuum, none of the spin-half particles could ever swap helicity. Therefore in the absence of some other cause, all fermions must be massless.</ref>) [[W and Z bosons]] are observed to have mass, but a boson mass term contains terms which clearly depend on the choice of gauge and therefore these masses too cannot be gauge invariant. Therefore it seems that ''none'' of the standard model fermions ''or'' bosons could "begin" with mass as an inbuilt property except by abandoning gauge invariance. If gauge invariance were to be retained, then these particles had to be acquiring their mass by some other mechanism or interaction. Additionally, whatever was giving these particles their mass, had to not "break" gauge invariance as the basis for other parts of the theories where it worked well, ''and'' had to not require or predict unexpected massless particles and long-range forces (seemingly an inevitable consequence of [[Goldstone's theorem]]) which did not actually seem to exist in nature.
 
A solution to all of these overlapping problems came from the discovery of a previously unnoticed borderline case hidden in the mathematics of Goldstone's theorem,<ref group="Note" name="GoldstoneNote">[[Goldstone's theorem]] only applies to gauges having [[Lorentz covariance|manifest Lorentz covariance]], a condition that took time to become questioned. But the process of [[quantization (physics)|quantisation]]<!--BRITISH ENGLISH SPELLING--> requires a [[gauge fixing|gauge to be fixed]] and at this point it becomes possible to choose a gauge such as the 'radiation' gauge which is not invariant over time, so that these problems can be avoided. According to Bernstein (1974, p.8):
: "the "radiation gauge" condition {{nowrap|1=∇⋅A(''x'') = 0}} is clearly noncovariant, which means that if we wish to maintain transversality of the photon in all [[Lorentz frame]]s, the [[photon field]] A<sub>μ</sub>(''x'') cannot transform like a [[four-vector]]. This is no catastrophe, since the photon ''field'' is not an [[observable]], and one can readily show that the S-matrix elements, which ''are'' observable have covariant structures .... in gauge theories one might arrange things so that one had a symmetry breakdown because of the noninvariance of the vacuum; but, because the Goldstone ''et al.'' proof breaks down, the zero mass Goldstone mesons need not appear." '''[Emphasis in original]'''
Bernstein (1974) contains an accessible and comprehensive background and review of this area, see [[#external links|external links]]</ref> that under certain conditions it ''might'' theoretically be possible for a symmetry to be broken ''without'' disrupting gauge invariance and ''without'' any new massless particles or forces, and having "sensible" ([[renormalization|renormalisable]]) results mathematically: this became known as the [[Higgs mechanism]].
 
The Standard Model hypothesizes a [[Quantum field theory|field]] which is responsible for this effect, called the Higgs field (symbol: <math>\phi</math>), which has the unusual property of a non-zero amplitude in its [[ground state]]; i.e., a non-zero [[vacuum expectation value]]. It can have this effect because of its unusual "Mexican hat" shaped potential whose lowest "point" is not at its "centre". Below a certain extremely high energy level the existence of this non-zero vacuum expectation [[symmetry breaking|spontaneously breaks]] [[electroweak interaction|electroweak]] [[Introduction to gauge theory|gauge symmetry]] which in turn gives rise to the Higgs mechanism and triggers the acquisition of mass by those particles interacting with the field. This effect occurs because [[scalar field]] components of the Higgs field are "absorbed" by the massive bosons as [[degrees of freedom (physics and chemistry)|degrees of freedom]], and couple to the fermions via [[Yukawa coupling]], thereby producing the expected mass terms. In effect when symmetry breaks under these conditions, the [[Goldstone boson]]s that arise ''interact'' with the Higgs field (and with other particles capable of interacting with the Higgs field) instead of becoming new massless particles, the intractable problems of both underlying theories "neutralise" each other, and the residual outcome is that elementary particles acquire a consistent mass based on how strongly they interact with the Higgs field. It is the simplest known process capable of giving mass to the [[gauge boson]]s while remaining compatible with [[gauge theories]].<ref>{{cite book
|title=Introduction to Quantum Field Theory
|last=Peskin
|first=Michael E.
|coauthors=Daniel V. Schroeder
|year=1995
|publisher=Addison-Wesley Publishing Company
|location=Reading, MA
|isbn=0-201-50397-2
|pages=717–719 and 787–791|ref=harv}}</ref> Its [[quantum]] would be a [[scalar boson|scalar]] [[boson]], known as the Higgs boson.<ref>{{harvnb|Peskin|Schroeder|1995|pp=715–716 }}</ref>
 
[[File:Elementary particle interactions.svg|250px|thumb|right|Summary of interactions between certain [[elementary particle|particles]] described by the [[Standard Model]].]]
 
=== Properties of the Standard Model Higgs ===
In the Standard Model, the Higgs field consists of four components, two neutral ones and two charged component [[field (physics)|fields]]. Both of the charged components and one of the neutral fields are [[Goldstone boson]]s, which act as the longitudinal third-polarization components of the massive [[W and Z bosons|W<sup>+</sup>, W<sup>–</sup>, and Z bosons]]. The quantum of the remaining neutral component corresponds to (and is theoretically realised as) the massive Higgs boson.<ref name=Gunion1>{{cite book
| last = Gunion
| first = John
| title = The Higgs Hunter's Guide
| publisher = Westview Press
| edition = illustrated, reprint
| year = 2000
| pages = 1–3
| isbn = 9780738203058
}}</ref> Since the Higgs field is a [[scalar field]] (meaning it does not transform under [[Lorentz transformation]]s), the Higgs boson has no [[spin (physics)|spin]]. The Higgs boson is also its own [[antiparticle]] and is [[CP-symmetry|CP-even]], and has zero [[Electric charge|electric]] and [[color charge|colour]] charge.<ref name=npr-interview>{{cite news|last=Flatow|first=Ira|title=At Long Last, The Higgs Particle... Maybe|url=http://www.npr.org/2012/07/06/156380366/at-long-last-the-higgs-particle-maybe|accessdate=10 July 2012|newspaper=NPR|date=6 July 2012}}</ref>
 
The Minimal Standard Model does not predict the mass of the Higgs boson.<ref name=atlas-higgs-diagrams>{{cite web|title=Explanatory Figures for the Higgs Boson Exclusion Plots|url=http://atlas.ch/news/2011/simplified-plots.html|work=ATLAS News|publisher=CERN|accessdate=6 July 2012}}</ref>  If that mass is between 115 and {{val|180|u=GeV/c2}}, then the Standard Model can be valid at energy scales all the way up to the [[Planck scale]] (10<sup>19</sup> GeV).<ref>{{cite web
| last = Bernardi
| first = G.
| last2 = Carena
| first2 = M.
| last3 = Junk
| first3 = T.
| title = Higgs Bosons: Theory and Searches
| page = 7
| year = 2012
| url = https://pdg.web.cern.ch/pdg/2012/reviews/rpp2012-rev-higgs-boson.pdf
| ref = harv}}</ref>  Many theorists expect new [[physics beyond the Standard Model]] to emerge at the TeV-scale, based on unsatisfactory properties of the Standard Model.<ref>{{cite conference
|arxiv=1005.1676
|title=Beyond the Standard Model
|last=Lykken |first=Joseph D.
|booktitle=Proceedings of the 2009 European School of High-Energy Physics, Bautzen, Germany, 14&nbsp;– 27 June 2009
|year=2009}}</ref> The highest possible mass scale allowed for the Higgs boson (or some other electroweak symmetry breaking mechanism) is 1.4 TeV; beyond this point, the Standard Model becomes inconsistent without such a mechanism, because [[Unitarity (physics)|unitarity]] is violated in certain scattering processes.<ref>{{cite book
|title = Lectures on LHC Physics
|first = Tilman |last=Plehn
|arxiv = 0910.4122
|series = Lecture Notes is Physics
|volume = 844
|year = 2012
|publisher = Springer
|isbn = 3642240399
|at=Sec. 1.2.2}}</ref>
 
It is also possible, although experimentally difficult, to estimate the mass of the Higgs boson indirectly. In the Standard Model, the Higgs boson has a number of indirect effects; most notably, Higgs loops result in tiny corrections to masses of W and Z bosons. Precision measurements of electroweak parameters, such as the [[Fermi's interaction|Fermi constant]] and masses of W/Z bosons, can be used to calculate constraints on the mass of the Higgs. As of July 2011, the precision electroweak measurements tell us that the mass of the Higgs boson is likely to be less than about {{val|161|u=GeV/c2}} at 95% [[confidence level]] (this upper limit would increase to {{val|185|u=GeV/c2}} if the lower bound of {{val|114.4|u=GeV/c2}} from the LEP-2 direct search is allowed for<ref name="EWWG" />). These indirect constraints rely on the assumption that the Standard Model is correct. It may still be possible to discover a Higgs boson above these masses if it is accompanied by other particles beyond those predicted by the Standard Model.<ref>{{cite journal
|title = How Can a Heavy Higgs Boson be Consistent with the Precision Electroweak Measurements?
|first1 = Michael E. |last1=Peskin
|first2 = James D. |last2=Wells
|journal = Physical Review D |volume=64 |year=2001 |page=093003
|arxiv = hep-ph/0101342
|doi = 10.1103/PhysRevD.64.093003
|bibcode = 2001PhRvD..64i3003P
|issue = 9
|ref = harv }}</ref>
 
=== Production ===
{| class="wikitable" style="float:right; margin:0 0 0 1em; text-align:center;"
|+ [[Feynman diagram]]s for Higgs production
|-
|[[File:Higgs-gluon-fusion.svg|frameless|upright=.7|Gluon fusion]]<br />''Gluon fusion''
|[[File:Higgs-Higgsstrahlung.svg|frameless|upright=.7|Higgs Strahlung]]<br />''Higgs Strahlung''
|-
|[[File:Higgs-WZ-fusion.svg|frameless|upright=.7|Vector boson fusion]]<br />''Vector boson fusion''
|[[File:Higgs-tt-fusion.svg|frameless|upright=.7|Top fusion]]<br />''Top fusion''
|}
 
If Higgs particle theories are correct, then a Higgs particle can be produced much like other particles that are studied, in a [[particle collider]]. This involves accelerating a large number of particles to extremely high energies and extremely close to the [[speed of light]], then allowing them to smash together. [[Proton]]s and [[lead]] [[ion]]s (the bare [[atomic nucleus|nuclei]] of lead [[atom]]s) are used at the LHC. In the extreme energies of these collisions, the desired esoteric particles will occasionally be produced and this can be detected and studied; any absence or difference from theoretical expectations can also be used to improve the theory. The relevant particle theory (in this case the Standard Model) will determine the necessary kinds of collisions and detectors. The Standard Model predicts that Higgs bosons could be formed in a number of ways,<ref name="HprodLHC">{{cite journal
|title=Higgs production at the lHC
|first1=Julien |last1=Baglio |first2=Abdelhak |last2=Djouadi
|journal=Journal of High Energy Physics |volume=1103 |year=2011 |page=055
|doi=10.1007/JHEP03(2011)055
|arxiv=1012.0530|bibcode = 2011JHEP...03..055B
|issue=3
|ref=harv }}</ref><ref name="HprodTeva">{{cite journal
|title=Predictions for Higgs production at the Tevatron and the associated uncertainties
|first1=Julien |last1=Baglio |first2=Abdelhak |last2=Djouadi
|journal=Journal of High Energy Physics |volume=1010 |year=2010 |page=063
|doi=10.1007/JHEP10(2010)064
|arxiv=1003.4266 |bibcode = 2010JHEP...10..064B
|issue=10
|ref=harv }}</ref><ref name="HprodLEP">{{cite journal
|title=Higgs boson searches at LEP
|first=P. |last=Teixeira-Dias (LEP Higgs working group)
|journal=Journal of.Physics: Conference Series |volume=110 |year=2008 |page=042030
|doi=10.1088/1742-6596/110/4/042030
|arxiv=0804.4146 |bibcode = 2008JPhCS.110d2030T
|issue=4
|ref=harv }}</ref> although the probability of producing a Higgs boson in any collision is always expected to be very small—for example, only 1 Higgs boson per 10 billion collisions in the Large Hadron Collider.{{#tag:ref|The example is based on the production rate at the LHC operating at 7 TeV. The total cross-section for producing a Higgs boson at the LHC is about 10 [[picobarn]],<ref name="HprodLHC"/> while the total cross-section for a proton–proton collision is 110 [[millibarn]].<ref>{{cite web
|url=http://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach/collisions.htm
|title=Collisions
|work=LHC Machine Outreach
|publisher=CERN
|accessdate=26 July 2012
}}</ref>|name="production_rate"|group="Note"}} The most common expected processes for Higgs boson production are:
* ''Gluon fusion''. If the collided particles are [[hadron]]s such as the [[proton]] or [[antiproton]]—as is the case in the LHC and Tevatron—then it is most likely that two of the [[gluon]]s binding the hadron together collide. The easiest way to produce a Higgs particle is if the two gluons combine to form a loop of [[virtual particle|virtual]] quarks. Since the coupling of particles to the Higgs boson is proportional to their mass, this process is more likely for heavy particles. In practice it is enough to consider the contributions of virtual [[top quark|top]] and [[bottom quark|bottom]] quarks (the heaviest quarks). This process is the dominant contribution at the LHC and Tevatron being about ten times more likely than any of the other processes.<ref name="HprodLHC"/><ref name="HprodTeva"/>
* ''Higgs Strahlung''. If an elementary [[fermion]] collides with an anti-fermion—e.g., a quark with an anti-quark or an [[electron]] with a [[positron]]—the two can merge to form a virtual W or Z boson which, if it carries sufficient energy, can then emit a Higgs boson.  This process was the dominant production mode at the LEP, where an electron and a positron collided to form a virtual Z boson, and it was the second largest contribution for Higgs production at the Tevatron. At the LHC this process is only the third largest, because the LHC collides protons with protons, making a quark-antiquark collision less likely than at the Tevatron.<ref name="HprodLHC"/><ref name="HprodTeva"/><ref name="HprodLEP"/>
* ''Weak boson fusion''. Another possibility when two (anti-)fermions collide is that the two exchange a virtual W or Z boson, which emits a Higgs boson. The colliding fermions do not need to be the same type. So, for example, an [[up quark]] may exchange a Z boson with an anti-down quark. This process is the second most important for the production of Higgs particle at the LHC and LEP.<ref name="HprodLHC"/><ref name="HprodLEP"/>
* ''Top fusion''. The final process that is commonly considered is by far the least likely (by two orders of magnitude). This process involves two colliding gluons, which each decay into a heavy quark–antiquark pair. A quark and antiquark from each pair can then combine to form a Higgs particle.<ref name="HprodLHC"/><ref name="HprodTeva"/>
 
=== Decay ===
[[File:Higgsdecaywidth.svg|thumb|upright=1.3|The Standard Model prediction for the [[decay width]] of the Higgs particle depends on the value of its mass.]]
Quantum mechanics predicts that if it is possible for a particle to decay into a set of lighter particles, then it will eventually do so.<ref>{{cite news
|url=http://www.guardian.co.uk/science/life-and-physics/2012/jun/22/higgs-boson-particlephysics
|title=Why does the Higgs decay?
|first=Lily |last=Asquith
|work=Life and Physics
|publisher=The Guardian
|date=22 June 2012
|accessdate=14 August 2012
|location=London
}}</ref>  This is also true for the Higgs boson. The likelihood with which this happens depends on a variety of factors including: the difference in mass, the strength of the interactions, etc. Most of these factors are fixed by the Standard Model, except for the mass of the Higgs boson itself. For a Higgs boson with a mass of {{val|126|u=GeV/c2}} the SM predicts a mean life time of about {{val|1.6|e=-22|u=s}}.{{#tag:ref|In the [[Standard Model]], the total [[decay width]] of a Higgs boson with a mass of {{val|126|u=GeV/c2}} is predicted to be {{val|4.21|e=-3|u=GeV}}.<ref name="LHCcrosssections">{{cite journal
|title=Handbook of LHC Higgs Cross Sections: 2. Differential Distributions
|author=LHC Higgs Cross Section Working Group
|journal=CERN Report 2 (Tables A.1 – A.20)
|arxiv=1201.3084
|bibcode = 2012arXiv1201.3084L
|ref=harv
|last2=Dittmaier
|last3=Mariotti
|last4=Passarino
|last5=Tanaka
|last6=Alekhin
|last7=Alwall
|last8=Bagnaschi
|last9=Banfi
|displayauthors=9
|volume=1201
|year=2012
|page=3084 }}</ref> The mean lifetime is given by <math>\tau = \hbar/\Gamma</math>.|group="Note"|name="meanlife"}}
 
[[File:HiggsBR.svg|thumb|upright=1.3|The Standard Model prediction for the [[branching ratio]]s of the different decay modes of the Higgs particle depends on the value of its mass.]]
Since it interacts with all the massive elementary particles of the SM, the Higgs boson has many different processes through which it can decay. Each of these possible processes has its own probability, expressed as the ''branching ratio''; the fraction of the total number decays that follows that process. The SM predicts these branching ratios as a function of the Higgs mass (see plot).
 
One way that the Higgs can decay is by splitting into a fermion–antifermion pair. As general rule, the Higgs is more likely to decay into heavy fermions than light fermions, because the mass of a fermion is proportional to the strength of its interaction with the Higgs.<ref name="PDGreview2012">{{cite web
|title=Higgs bosons: theory and searches
|url=http://pdg.lbl.gov/2012/reviews/rpp2012-rev-higgs-boson.pdf
|work=PDGLive
|publisher=Particle Data Group
|date=12 July 2012
|accessdate=15 August 2012
}}</ref> By this logic the most common decay should be into a [[top quark|top]]–antitop quark pair. However, such a decay is only possible if the Higgs is heavier than ~{{val|346|u=GeV/c2}}, twice the mass of the top quark. For a Higgs mass of {{val|126|u=GeV/c2}} the SM predicts that the most common decay is into a [[bottom quark|bottom]]–antibottom quark pair, which happens 56.1% of the time.<ref name="LHCcrosssections"/> The second most common fermion decay at that mass is a [[tau particle|tau]]–antitau pair, which happens only about 6% of the time.<ref name="LHCcrosssections"/>
 
Another possibility is for the Higgs to split into a pair of massive gauge bosons. The most likely possibility is for the Higgs to decay into a pair of W bosons (the light blue line in the plot), which happens about 23.1% of the time for a Higgs boson with a mass of {{val|126|u=GeV/c2}}.<ref name="LHCcrosssections"/> The W bosons can subsequently decay either into a quark and an antiquark or into a charged lepton and a neutrino. However, the decays of W bosons into quarks are difficult to distinguish from the background, and the decays into leptons cannot be fully reconstructed (because neutrinos are impossible to detect in particle collision experiments). A cleaner signal is given by decay into a pair of Z-bosons (which happens about 2.9% of the time for a Higgs with a mass of {{val|126|u=GeV/c2}}),<ref name="LHCcrosssections"/>  if each of the bosons subsequently decays into a pair of easy-to-detect charged leptons ([[electron]]s or [[muon]]s).
 
Decay into massless gauge bosons (i.e., [[gluon]]s or [[photon]]s) is also possible, but requires intermediate loop of virtual heavy quarks (top or bottom) or massive gauge bosons.<ref name="PDGreview2012"/> The most common such process is the decay into a pair of gluons through a loop of virtual heavy quarks. This process, which is the reverse of the gluon fusion process mentioned above, happens approximately 8.5% of the time for a Higgs boson with a mass of {{val|126|u=GeV/c2}}.<ref name="LHCcrosssections"/> Much rarer is the decay into a pair of photons mediated by a loop of W bosons or heavy quarks, which happens only twice for every thousand decays.<ref name="LHCcrosssections"/> However, this process is very relevant for experimental searches for the Higgs boson, because the energy and momentum of the photons can be measured very precisely, giving an accurate reconstruction of the mass of the decaying particle.<ref name="PDGreview2012"/>
 
=== Alternative models ===
{{main|Alternatives to the Standard Model Higgs}}
 
The Minimal Standard Model as described above is the simplest known model for the Higgs mechanism with just one Higgs field. However, an extended Higgs sector with additional Higgs particle doublets or triplets is also possible, and many extensions of the Standard Model have this feature. The non-minimal Higgs sector favoured by theory are the two-Higgs-doublet models (2HDM), which predict the existence of a [[quintet]] of scalar particles: two [[CP violation|CP-even]] neutral Higgs bosons h<sup>0</sup> and H<sup>0</sup>, a CP-odd neutral Higgs boson A<sup>0</sup>, and two charged Higgs particles H<sup>±</sup>. [[Supersymmetry]] ("SUSY") also predicts relations between the Higgs-boson masses and the masses of the gauge bosons, and could accommodate a {{val|125|u=GeV/c2}} neutral Higgs boson.
 
The key method to distinguish between these different models involves study of the particles' interactions ("coupling") and exact decay processes ("branching ratios"), which can be measured and tested experimentally in particle collisions. In the Type-I 2HDM model one Higgs doublet couples to up and down quarks, while the second doublet does not couple to quarks. This model has two interesting limits, in which the lightest Higgs couples to just fermions ("gauge-[[phobia|phobic]]") or just gauge bosons ("fermiophobic"), but not both. In the Type-II 2HDM model, one Higgs doublet only couples to up-type quarks, the other only couples to down-type quarks.<ref>{{cite journal
| last = Branco
| first = G. C.
| title = Theory and phenomenology of two-Higgs-doublet models
| journal = Physics Reports
| volume = 516
| issue = 1
| pages = 1–102
| publisher = Elsevier
| date = 07/2012
| doi = 10.1016/j.physrep.2012.02.002
|bibcode = 2012PhR...516....1B |arxiv = 1106.0034
| last2 = Ferreira
| first2 = P.M.
| last3 = Lavoura
| first3 = L.
| last4 = Rebelo
| first4 = M.N.
| last5 = Sher
| first5 = Marc
| last6 = Silva
| first6 = João P.
| ref = harv }}</ref> The heavily researched [[Minimal Supersymmetric Standard Model]] (MSSM) includes a Type-II 2HDM Higgs sector, so it could be disproven by evidence of a Type-I 2HDM Higgs.{{citation needed|date=July 2012}}
 
In other models the Higgs scalar is a composite particle. For example, in [[Technicolor (physics)|technicolor]] the role of the Higgs field is played by strongly bound pairs of fermions called [[techniquark]]s. Other models, feature pairs of [[top quark]]s (see [[top quark condensate]]). In yet other models, there is [[Higgsless model|no Higgs field at all]] and the electroweak symmetry is broken using extra dimensions.<ref>{{Cite journal |first=C. |last=Csaki |first2=C. |last2=Grojean |first3=L. |last3=Pilo |first4=J. |last4=Terning |year=2004|title=Towards a realistic model of Higgsless electroweak symmetry breaking |journal=[[Physical Review Letters]] |volume=92 |issue=10 |page=101802 |doi=10.1103/PhysRevLett.92.101802  |pmid=15089195 |arxiv=hep-ph/0308038 |bibcode=2004PhRvL..92j1802C |ref=harv}}</ref><ref>{{Cite journal |first=C. |last=Csaki |first2=C. |last2=Grojean |first3=L. |last3=Pilo |first4=J. |last4=Terning |year=2004 |title=Gauge theories on an interval: Unitarity without a Higgs |journal=[[Physical Review D]] |volume=69 |issue=5 |page=055006 |doi=10.1103/PhysRevD.69.055006  |last5=Terning |first5=John |arxiv=hep-ph/0305237|bibcode = 2004PhRvD..69e5006C |ref=harv}}</ref>
 
[[File:One-loop-diagram.svg|thumb|A one-loop [[Feynman diagram]] of the first-order correction to the Higgs mass. In the Standard Model the effects of these corrections are potentially enormous, giving rise to the so-called [[hierarchy problem]].]]
 
=== Further theoretical issues and hierarchy problem ===
{{Main|Hierarchy problem|Hierarchy problem#The Higgs mass}}
The Standard Model leaves the mass of the Higgs boson as a [[parameter]] to be measured, rather than a value to be calculated. This is seen as theoretically unsatisfactory, particularly as quantum corrections (related to interactions with [[virtual particle]]s) should apparently cause the Higgs particle to have a mass immensely higher than that observed, but at the same time the Standard Model requires a mass [[order of magnitude|of the order of]] 100 to 1000 GeV to ensure [[unitarity]] (in this case, to unitarise longitudinal vector boson scattering).<ref name="Hierarchy problem Quantum Diaries">{{cite web|title=The Hierarchy Problem: why the Higgs has a snowball's chance in hell|url=http://www.quantumdiaries.org/2012/07/01/the-hierarchy-problem-why-the-higgs-has-a-snowballs-chance-in-hell/|publisher=Qyuantum Diaries|accessdate=19 March 2013|date=2012-07-01}}</ref> Reconciling these points appears to require explaining why there is an almost-perfect cancellation resulting in the visible mass of ~ 125 GeV, and it is not clear how to do this. Because the weak force is about 10<sup>32</sup> times stronger than gravity, and (linked to this) the Higgs boson's mass is so much less than the [[Planck mass]] or the [[grand unification energy]], it appears that either there is some underlying connection or reason for these observations which is unknown and not described by the Standard Model, or some unexplained and extremely precise [[fine-tuning]] of parameters – however at present neither of these explanations is proven. This is known as a [[hierarchy problem]].<ref>{{cite web|url=http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-hierarchy-problem/ |title=The Hierarchy Problem &#124; Of Particular Significance |publisher=Profmattstrassler.com |date= |accessdate=2013-10-09}}</ref> More broadly, the hierarchy problem amounts to the worry that [[physics beyond the standard model|a future theory of fundamental particles and interactions]] should not have excessive fine-tunings or unduly delicate cancellations, and should allow masses of particles such as the Higgs boson to be calculable. The problem is in some ways unique to spin-0 particles (such as the Higgs boson), which can give rise to issues related to quantum corrections that do not affect particles with spin.<ref name="Hierarchy problem Quantum Diaries" /> A [[Hierarchy problem#Theoretical solutions|number of solutions have been proposed]], including [[supersymmetry]], conformal solutions and solutions via extra dimensions such as [[braneworld]] models.
 
== Experimental search ==
{{main|Search for the Higgs boson}}
To [[#Production|produce Higgs bosons]], two beams of particles are accelerated to very high energies and allowed to collide within a [[particle detector]]. Occasionally, although rarely, a Higgs boson will be created fleetingly as part of the collision byproducts. Because the Higgs boson [[#Decay|decays]] very quickly, particle detectors cannot detect it directly. Instead the detectors register all the decay products (the ''decay signature'') and from the data the decay process is reconstructed. If the observed decay products match a possible decay process (known as a ''decay channel'') of a Higgs boson, this indicates that a Higgs boson may have been created. In practice, many processes may produce similar decay signatures. Fortunately, the Standard Model precisely predicts the likelihood of each of these, and each known process, occurring. So, if the detector detects more decay signatures consistently matching a Higgs boson than would otherwise be expected if Higgs bosons did not exist, then this would be strong evidence that the Higgs boson exists.
 
Because Higgs boson production in a particle collision is likely to be very rare (1 in 10 billion at the LHC),<ref name="production_rate" group="Note"/> and many other possible collision events can have similar decay signatures, the data of hundreds of trillions of collisions needs to be analysed and must "show the same picture" before a conclusion about the existence of the Higgs boson can be reached. To conclude that a new particle has been found, [[particle physicist]]s require that the [[statistical analysis]] of two independent particle detectors each indicate that there is lesser than a one-in-a-million chance that the observed decay signatures are due to just background random Standard Model events—i.e., that the observed number of events is more than 5 [[standard deviation]]s (sigma) different from that expected if there was no new particle. More collision data allows better confirmation of the physical properties of any new particle observed, and allows physicists to decide whether it is indeed a Higgs boson as described by the Standard Model or some other hypothetical new particle.
 
To find the Higgs boson, a powerful [[particle accelerator]] was needed, because Higgs bosons might not be seen in lower-energy experiments. The collider needed to have a high [[Luminosity#Scattering theory|luminosity]] in order to ensure enough collisions were seen for conclusions to be drawn. Finally, advanced computing facilities were needed to process the vast amount of data (25 [[petabyte]]s per year as at 2012) produced by the collisions.<ref name="msnbc-discovery"/> For the announcement of 4 July 2012, a new collider known as the [[Large Hadron Collider]] was constructed at [[CERN]] with a planned eventual collision energy of 14 [[TeV]]—over seven times any previous collider—and over 300 trillion (3×10<sup>14</sup>) LHC proton–proton collisions were analysed by the [[LHC Computing Grid]], the world's largest [[computing grid]] (as of 2012), comprising over 170 computing facilities in a [[distributed computing|worldwide network]] across 36 countries.<ref name="msnbc-discovery"/><ref>[http://wlcg.web.cern.ch/ Worldwide LHC Computing Grid main page] 14 November 2012: ''"[A] global collaboration of more than 170 computing centres in 36 countries ... to store, distribute and analyse the ~25 Petabytes (25 million Gigabytes) of data annually generated by the Large Hadron Collider"''</ref><ref>[http://lcg-archive.web.cern.ch/lcg-archive/public/overview.htm What is the Worldwide LHC Computing Grid? (Public 'About' page)] 14 November 2012: ''"Currently WLCG is made up of more than 170 computing centers in 36 countries...The WLCG is now the world's largest computing grid"''</ref>
 
=== Search prior to 4 July 2012 ===
The first extensive search for the Higgs boson was conducted at the [[Large Electron–Positron Collider]] (LEP) at CERN in the 1990s. At the end of its service in 2000, LEP had found no conclusive evidence for the Higgs.<ref group="Note">Just before LEP's shut down, some events that hinted at a Higgs were observed, but it was not judged significant enough to extend its run and delay construction of the LHC.</ref> This implied that if the Higgs boson were to exist it would have to be heavier than {{val|114.4|u=GeV/c2}}.<ref name="Yao 2006">{{cite journal|author=W.-M. Yao|year=2006|title=Review of Particle Physics|url=http://pdg.lbl.gov/2006/reviews/higgs_s055.pdf Searches for Higgs Bosons|journal=[[Journal of Physics G]]|volume=33 |issue= |page=1|arxiv = astro-ph/0601168|bibcode = 2006JPhG...33....1Y|doi=10.1088/0954-3899/33/1/001|author-separator=,|display-authors=1|author2=<Please add first missing authors to populate metadata.>|ref=harv}}</ref>
 
The search continued at [[Fermilab]] in the United States, where the [[Tevatron]]—the collider that discovered the [[top quark]] in 1995—had been upgraded for this purpose. There was no guarantee that the Tevatron would be able to find the Higgs, but it was the only supercollider that was operational since the [[Large Hadron Collider]] (LHC) was still under construction and the planned [[Superconducting Super Collider]] had been cancelled in 1993 and never completed. The Tevatron was only able to exclude further ranges for the Higgs mass, and was shut down on 30 September 2011 because it no longer could keep up with the LHC. The final analysis of the data excluded the possibility of a Higgs boson with a mass between {{val|147|u=GeV/c2}} and {{val|180|u=GeV/c2}}. In addition, there was a small (but not significant) excess of events possibly indicating a Higgs boson with a mass between {{val|115|u=GeV/c2}} and {{val|140|u=GeV/c2}}.<ref>{{cite arXiv|title=Updated Combination of CDF and D0 Searches for Standard Model Higgs Boson Production with up to {{val|10.0|u=fb-1}} of Data|author=The CDF Collaboration, the D0 Collaboration, the Tevatron New Physics, Higgs Working Group|eprint=1207.0449|class=hep-ex|year=2012}}</ref>
 
The [[Large Hadron Collider]] at [[CERN]] in [[Switzerland]], was designed specifically to be able to either confirm or exclude the existence of the Higgs boson. Built in a 27&nbsp;km tunnel under the ground near [[Geneva]] originally inhabited by LEP, it was designed to collide two beams of protons, initially at energies of {{val|3.5|u=TeV}} per beam (7&nbsp;TeV total), or almost 3.6 times that of the Tevatron, and upgradeable to {{nowrap|2 × 7 TeV}} (14&nbsp;TeV total) in future. Theory suggested if the Higgs boson existed, collisions at these energy levels should be able to reveal it. As one of the [[List of megaprojects#Science projects|most complicated scientific instruments]] ever built, its operational readiness was delayed for 14 months by a [[Magnet quench|magnet quench event]] nine days after its inaugural tests, caused by a faulty electrical connection that damaged over 50 superconducting magnets and contaminated the vacuum system.<ref>
{{cite web|date=15 October 2008|title=Interim Summary Report on the Analysis of the 19 September 2008 Incident at the LHC|url= https://edms.cern.ch/file/973073/1/Report_on_080919_incident_at_LHC__2_.pdf|format=PDF|publisher=[[CERN]]|id=EDMS&nbsp;973073|accessdate=28 September 2009}}</ref><ref>{{cite press|date=16 October 2008|title=CERN releases analysis of LHC incident|url=http://press.web.cern.ch/press/PressReleases/Releases2008/PR14.08E.html|publisher=CERN Press Office|accessdate=28 September 2009}}</ref><ref name="CERNsummer">{{cite press|date=5 December 2008|title=LHC to restart in 2009|url=http://press.web.cern.ch/press/PressReleases/Releases2008/PR17.08E.html|publisher=CERN Press Office|accessdate=8 December 2008}}</ref>
 
Data collection at the LHC finally commenced in March 2010.<ref>{{cite web|url=http://cdsweb.cern.ch/journal/CERNBulletin/2010/18/News%20Articles/1262593|title=LHC progress report|work=The Bulletin|publisher=CERN |date=3 May 2010 |accessdate=7 December 2011}}</ref> By December 2011 the two main particle detectors at the LHC, [[ATLAS experiment|ATLAS]] and [[Compact Muon Solenoid|CMS]], had narrowed down the mass range where the Higgs could exist to around 116-130 GeV (ATLAS) and 115-127 GeV (CMS).<ref name="ATLAS-13Dec2011">{{cite web|url=http://www.atlas.ch/news/2011/status-report-dec-2011.html|title=ATLAS experiment presents latest Higgs search status|work=ATLAS homepage|publisher=CERN|date=13 December 2011|accessdate=13 December 2011}}</ref><ref name="CMS_December 2011">{{cite web|first=Lucas |last=Taylor|url=http://cms.web.cern.ch/news/cms-search-standard-model-higgs-boson-lhc-data-2010-and-2011|title=CMS search for the Standard Model Higgs Boson in LHC data from 2010 and 2011|work=CMS public website|publisher=CERN |date=13 December 2011|accessdate=13 December 2011}}</ref>  There had  also already been a number of promising event excesses that had "evaporated" and proven to be nothing but random fluctuations. However from around May 2011,<ref name="NYT-20130305"/> both experiments had seen among their results, the slow emergence of a small yet consistent excess of gamma and 4-lepton decay signatures and several other particle decays, all hinting at a new particle at a mass around {{val|125|u=GeV}}.<ref name="NYT-20130305"/> By around November 2011, the anomalous data at 125&nbsp;GeV was becoming "too large to ignore" (although still far from conclusive), and the team leaders at both ATLAS and CMS each privately suspected they might have found the Higgs.<ref name="NYT-20130305"/> On November 28, 2011, at an internal meeting of the two team leaders and the director general of CERN, the latest analyses were discussed outside their teams for the first time, suggesting both ATLAS and CMS might be converging on a possible shared result at 125&nbsp;GeV, and initial preparations commenced in case of a successful finding.<ref name="NYT-20130305"/> While this information was not known publicly at the time, the narrowing of the possible Higgs range to around 115–130 GeV and the repeated observation of small but consistent event excesses across multiple channels at both ATLAS and CMS in the 124-126 GeV region (described as "tantalising hints" of around 2-3 sigma) were public knowledge with "a lot of interest".<ref name="CERN 13 dec 2011">{{cite press|date=13 December 2011|title=ATLAS and CMS experiments present Higgs search status|url=http://press.web.cern.ch/press-releases/2011/12/atlas-and-cms-experiments-present-higgs-search-status|publisher=CERN Press Office|quote=the statistical significance is not large enough to say anything conclusive. As of today what we see is consistent either with a background fluctuation or with the presence of the boson. Refined analyses and additional data delivered in 2012 by this magnificent machine will definitely give an answer|accessdate=14 September 2012}}</ref> It was therefore widely anticipated around the end of 2011, that the LHC would provide sufficient data to either exclude or confirm the finding of a Higgs boson by the end of 2012, when their 2012 collision data (with slightly higher 8&nbsp;TeV collision energy) had been examined.<ref name="CERN 13 dec 2011" /><ref>{{cite web|url=http://lcg-archive.web.cern.ch/lcg-archive/public/|title=WLCG Public Website|publisher=CERN|accessdate=29 October 2012}}</ref>
 
=== Discovery of candidate boson at CERN ===
{| class="wikitable" style="float:right; clear:right; margin-top:0; margin-left:10px; margin-bottom:8px; margin-right:0; padding:7px; font-size:85%; width:230px;"
|-
| {{nowrap|[[File:2-photon Higgs decay.svg|x110px]]&nbsp;&nbsp;[[File:4-lepton Higgs decay.svg|x110px]]}}
|-
| [[Feynman diagram]]s showing the cleanest channels associated with the Low-Mass, ~125GeV, Higgs Candidate observed by [[ATLAS experiment|ATLAS]] and [[Compact Muon Solenoid|CMS]] at the [[Large Hadron Collider|LHC]]. The dominant production mechanism at this mass involves two [[gluons]] from each proton fusing to a [[Top quark|Top-quark Loop]], which couples strongly to the Higgs Field to produce a Higgs Boson.
 
''Left:'' Diphoton Channel: Boson subsequently decays into 2 gamma ray photons by virtual interaction with a [[W and Z bosons|W Boson Loop]] or [[Top quark|Top-quark Loop]].
 
''Right:'' 4-Lepton "Golden Channel" Boson emits 2 [[W and Z bosons|Z bosons]], which each decay into 2 [[leptons]] (electrons,muons).
 
Experimental Analysis of these channels reached a significance of 5-[[standard deviation|sigma]].<ref name=cms0731/><ref name=cms1207 />
The analysis of additional [[W and Z bosons|vector boson fusion]] channels brought the [[Compact Muon Solenoid|CMS]] significance to 4.9-[[standard deviation|sigma]].<ref name=cms0731/><ref name=cms1207 />
|}
 
On 22 June 2012 [[CERN]] announced an upcoming seminar covering tentative findings for 2012,<ref name="autogenerated1">{{cite web|url=http://indico.cern.ch/conferenceDisplay.py?confId=196564 |title=Press Conference: Update on the search for the Higgs boson at CERN on 4 July 2012|publisher=Indico.cern.ch|date=22 June 2012|accessdate=4 July 2012}}</ref><ref name="autogenerated2">{{cite news |url= http://press.web.cern.ch/press/PressReleases/Releases2012/PR16.12E.html|title=CERN to give update on Higgs search|publisher=CERN|date=22 June 2012|accessdate=2 July 2011}}</ref> and shortly afterwards (from around 1 July 2012 according to an analysis of the spreading rumour in [[social media]]<ref>{{cite news|title=Scientists analyse global Twitter gossip around Higgs boson discovery|url=http://phys.org/news/2013-01-scientists-analyse-global-twitter-gossip.html|accessdate=6 February 2013|newspaper=phys.org (from arXiv)|date=2013-01-23}} – stated to be ''" the first time scientists have been able to analyse the dynamics of social media on a global scale before, during and after the announcement of a major scientific discovery."'' For the paper itself see: {{cite journal|last1=De Domenico |first1=M. |title=The Anatomy of a Scientific Gossip|year=2013|arxiv=1301.2952|ref=harv|bibcode=2013NatSR...3E2980D|doi=10.1038/srep02980|last2=Lima|first2=A.|last3=Mougel|first3=P.|last4=Musolesi|first4=M.|volume=|page=}}</ref>) rumours began to spread in the media that this would include a major announcement, but it was unclear whether this would be a stronger signal or a formal discovery.<ref name="timeslive1">{{cite web|url=http://www.timeslive.co.za/scitech/2012/06/28/higgs-boson-particle-results-could-be-a-quantum-leap |title=Higgs boson particle results could be a quantum leap|publisher=Times LIVE|date=28 June 2012|accessdate=4 July 2012}}</ref><ref>[http://www.abc.net.au/news/2012-07-04/cern-prepares-to-deliver-higgs-particle-findings/4108622 CERN prepares to deliver Higgs particle findings], Australian Broadcasting Corporation. Retrieved 4 July 2012.</ref> Speculation escalated to a "fevered" pitch when reports emerged that [[Peter Higgs]], who proposed the particle, was to be attending the seminar,<ref>{{cite web|author= |url=http://www.huffingtonpost.co.uk/2012/07/03/god-particle-finally-discovered-peter-higgs_n_1645865.html |title=God Particle Finally Discovered? Higgs Boson News At Cern Will Even Feature Scientist It's Named After |publisher=Huffingtonpost.co.uk |date= |accessdate=2013-01-19}}</ref><ref>{{cite news|author=Our Bureau |url=http://www.telegraphindia.com/1120704/jsp/frontpage/story_15689014.jsp |title=Higgs on way, theories thicken |publisher=Telegraphindia.com |date=2012-07-04 |accessdate=2013-01-19 |location=Calcutta, India}}</ref> and that "five leading physicists" had been invited – generally believed to signify the five living 1964 authors – with Higgs, Englert, Guralnik, Hagen attending and Kibble confirming his invitation (Brout having died in 2011).<ref>{{cite news|title=Higgs en route for CERN|url=http://blog.vixra.org/2012/07/02/higgs-en-route-for-cern/|accessdate=23 July 2013|newspaper=[[viXra]] blog|date=2013-07-02}}</ref><ref>{{cite news|last=Thornhill|first=Ted|title=God Particle Finally Discovered? Higgs Boson News At Cern Will Even Feature Scientist It's Named After|url=http://www.huffingtonpost.co.uk/2012/07/03/god-particle-finally-discovered-peter-higgs_n_1645865.html|accessdate=23 July 2013|newspaper=Huffington Post|date=2013-07-03}}</ref><ref>{{cite news|last=Cooper|first=Rob|title=God particle is 'found': Scientists at Cern expected to announce on Wednesday Higgs boson particle has been discovered|url=http://www.dailymail.co.uk/sciencetech/article-2167188/God-particle-Scientists-Cern-expected-announce-Higgs-boson-particle-discovered-Wednesday.html|accessdate=23 July 2013|date=2013-07-01 (updated subsequently)|location=London|work=Daily Mail}} - States that "''"Five leading theoretical physicists have been invited to the event on Wednesday - sparking speculation that the particle has been discovered."'', including Higgs and Englert, and that Kibble - who was invited but unable to attend - "told the [[Sunday Times]]: 'My guess is that is must be a pretty positive result for them to be asking us out there'."</ref>)
 
On 4 July 2012 both of the CERN experiments announced they had independently made the same discovery:<ref name=discovery>{{cite journal|author= Adrian Cho|title=Higgs Boson Makes Its Debut After Decades-Long Search|journal=Science|pages=141–143|volume=337|date=13 July 2012|doi= 10.1126/science.337.6091.141|pmid= 22798574|issue= 6091|ref= harv}}</ref> CMS of a previously unknown boson with mass 125.3 ± 0.6 GeV/''c''<sup>2</sup><ref name=cms0731/><ref name=cms1207>{{cite web|url=http://cms.web.cern.ch/news/observation-new-particle-mass-125-gev|title=Observation of a New Particle with a Mass of 125 GeV|first=Lucas|last=Taylor|date=4 July 2012|work=CMS Public Website|publisher=CERN|accessdate=4 July 2012}}</ref> and ATLAS of a boson with mass 126.5 GeV/''c''<sup>2</sup>.<ref name=atlas1207>{{cite web|title=Latest Results from ATLAS Higgs Search|url=http://www.atlas.ch/news/2012/latest-results-from-higgs-search.html|work=ATLAS News|publisher=CERN|date=4 July 2012|accessdate=4 July 2012}}</ref><ref name=atlas1207c>{{cite journal|author=ATLAS collaboration|title=Observation of an Excess of Events in the Search for the Standard Model Higgs boson with the ATLAS detector at the LHC|journal=Atlas-Conf-2012-093|volume=|issue=|pages=|doi=|year=2012|arxiv=|url=http://cdsweb.cern.ch/record/1460439|ref=harv}}</ref>
Using the combined analysis of two interaction types (known as 'channels'), both experiments reached a local significance of 5-sigma—or less than a 1 in one million chance of error. When additional channels were taken into account, the CMS significance was reduced to 4.9-sigma.<ref name=cms1207 />
 
The two teams had been working 'blinded' from each other from around late 2011 or early 2012,<ref name="NYT-20130305"/><!-- The source is somewhat ambiguous as to the exact date—it states the teams "blinded" themselves following the (November 2011) meeting, but provides this information in the section titled "January 2012"''--> meaning they did not discuss their results with each other, providing additional certainty that any common finding was genuine validation of a particle.<ref name="msnbc-discovery">{{cite web|author=|url=http://www.msnbc.msn.com/id/47783507/ns/technology_and_science-science/t/hunt-higgs-boson-hits-key-decision-point |title=Hunt for Higgs boson hits key decision point|publisher=MSNBC |date=2012-12-06 |accessdate=2013-01-19}}</ref> This level of evidence, confirmed independently by two separate teams and experiments, meets the formal level of proof required to announce a confirmed discovery.
 
On 31 July 2012, the ATLAS collaboration presented additional data analysis on the "observation of a new particle", including data from a third channel, which improved the significance to {{nowrap|5.9-sigma (1 in 588 million chance of being due to random background effects)}} and mass {{nowrap|126.0 ± 0.4 (stat) ± 0.4 (sys) GeV/''c''<sup>2</sup>}},<ref name=atlas0731 /> and CMS improved the significance to 5-sigma and mass {{nowrap|125.3 ± 0.4 (stat) ± 0.5 (sys) GeV/''c''<sup>2</sup>}}.<ref name=cms0731 />
 
=== The new particle tested as a possible Higgs boson ===
Following the 2012 discovery, it was still unconfimed whether or not the 125 GeV/''c''<sup>2</sup> particle was a Higgs boson. On one hand, observations remained consistent with the observed particle being the Standard Model Higgs boson, and the particle decayed into at least some of the predicted channels. Moreover, the production rates and branching ratios for the observed channels broadly matched the predictions by the Standard Model within the experimental uncertainties. However, the experimental uncertainties currently still left room for alternative explanations, meaning an announcement of the discovery of a Higgs boson would have been premature.<ref name="PDGreview2012"/> To allow more opportunity for data collection, the LHC's proposed 2012 shutdown and 2013–14 upgrade were postponed by 7 weeks into 2013.<ref>{{cite web|title=LHC 2012 proton run extended by seven weeks|url=http://cdsweb.cern.ch/journal/CERNBulletin/2012/30/News%20Articles/1462536?ln=en|first=James|last=Gillies|work=CERN bulletin|date=23 July 2012|accessdate=29 August 2012}}</ref>
 
In November 2012, in a conference in Kyoto researchers said evidence gathered since July was falling into line with the basic Standard Model more than its alternatives, with a range of results for several interactions matching that theory's predictions.<ref name="BBC Nov 2012">{{cite news|url=http://www.3news.co.nz/Higgs-boson-behaving-as-expected/tabid/1160/articleID/276802/Default.aspx |work=3 News NZ| title= Higgs boson behaving as expected| date=15 November 2012}}</ref> Physicist Matt Strassler highlighted "considerable" evidence that the new particle is not a [[pseudoscalar]] [[Parity (physics)|negative parity]] particle (consistent with this required finding for a Higgs boson), "evaporation" or lack of increased significance for previous hints of non-Standard Model findings, expected Standard Model interactions with [[W and Z bosons]], absence of "significant new implications" for or against [[supersymmetry]], and in general no significant deviations to date from the results expected of a Standard Model Higgs boson.<ref name="strassler nov 2012">{{cite web|last=Strassler|first=Matt|title=Higgs Results at Kyoto|url=http://profmattstrassler.com/2012/11/14/higgs-results-at-kyoto/|work=Of Particular Significance: Conversations About Science with Theoretical Physicist Matt Strassler|publisher=Prof. Matt Strassler's personal particle physics website|accessdate=10 January 2013|date=2012-11-14|quote=ATLAS and CMS only just co-discovered this particle in July ... We will not know after today whether it is a Higgs at all, whether it is a Standard Model Higgs or not, or whether any particular speculative idea...is now excluded. [...] Knowledge about nature does not come easy.  We discovered the top quark in 1995, and we are still learning about its properties today... we will still be learning important things about the Higgs during the coming few decades.  We’ve no choice but to be patient.}}</ref> However some kinds of extensions to the Standard Model would also show very similar results;<ref name="Guardian Nov 2012">{{cite news|last=Sample|first=Ian|title=Higgs particle looks like a bog Standard Model boson, say scientists|url=http://www.guardian.co.uk/science/2012/nov/14/higgs-standard-model-boson|accessdate=15 November 2012|newspaper=The Guardian|date=14 November 2012|location=London}}</ref> so commentators noted that based on other particles that are still being understood long after their discovery, it may take years to be sure, and decades to fully understand the particle that has been found.<ref name="BBC Nov 2012" /><ref name="strassler nov 2012" />
 
These findings meant that as of January 2013, scientists were very sure they had found an unknown particle of mass ~ 125&nbsp;GeV/''c''<sup>2</sup>, and had not been misled by experimental error or a chance result. They were also sure, from initial observations, that the new particle was some kind of boson. The behaviours and properties of the particle, so far as examined since July 2012, also seemed quite close to the behaviours expected of a Higgs boson. Even so, it could still have been a Higgs boson or some other unknown boson, since future tests could show behaviours that do not match a Higgs boson, so as of December 2012 CERN still only stated that the new particle was "consistent with" the Higgs boson,<ref name="dieter July 2012" /><ref name="CERN Nov 2012" /> and scientists did not yet positively say it was the Higgs boson.<ref name=cern1207>{{cite news |url=http://press.web.cern.ch/press/PressReleases/Releases2012/PR17.12E.html |title=CERN experiments observe particle consistent with long-sought Higgs boson |publisher=CERN press release |date=4 July 2012 |accessdate=4 July 2012}}</ref> Despite this, in late 2012, widespread media reports announced (incorrectly) that a Higgs boson had been confirmed during the year.{{#tag:ref|''[[Time (magazine)|Time]]'',<ref>{{cite news| url=http://poy.time.com/2012/12/19/the-higgs-boson-particle-of-the-year/ | work=Time | title=Person Of The Year 2012 | date=19 December 2012}}</ref> [[Forbes]],<ref>{{cite web|url=http://www.forbes.com/sites/alexknapp/2012/09/12/higgs-boson-discovery-has-been-confirmed/ |title=Higgs Boson Discovery Has Been Confirmed |publisher=Forbes |date= |accessdate=2013-10-09}}</ref> ''[[Slate (magazine)|Slate]]'',<ref>{{cite web|last=Staff |first=Slate V |url=http://www.slate.com/blogs/trending/2012/09/11/higgs_boson_confirmed_cern_discovery_passes_test.html |title=Higgs Boson Confirmed; CERN Discovery Passes Test |publisher=Slate.com |date=2012-09-11 |accessdate=2013-10-09}}</ref> ''[[NPR]]'',<ref>{{cite web|url=http://www.npr.org/2013/01/01/168208273/the-year-of-the-higgs-and-other-tiny-advances-in-science |title=The Year Of The Higgs, And Other Tiny Advances In Science |publisher=NPR |date=2013-01-01 |accessdate=2013-10-09}}</ref> and others<ref>{{cite news| url=http://www.smh.com.au/world/science/confirmed-the-higgs-boson-does-exist-20120704-21hac.html | work=The Sydney Morning Herald | title=Confirmed: the Higgs boson does exist | date=4 July 2012}}</ref>}}
 
In January 2013, CERN director-general [[Rolf-Dieter Heuer]] stated that based on data analysis to date, an answer could be possible 'towards' mid-2013,<ref name="status Jan 2013">{{cite news|title=AP CERN chief: Higgs boson quest could wrap up by midyear|url=http://www.nbcnews.com/id/50601148/ns/technology_and_science-science/#.USVTVx287-Y|accessdate=20 February 2013|newspaper=MSNBC|date=2013-01-27|agency=Associated Press|quote=Rolf Heuer, director of [CERN], said he is confident that "towards the middle of the year, we will be there."}} – Interview by AP, at the World Economic Forum, 26 Jan 2013.</ref> and the deputy chair of physics at [[Brookhaven National Laboratory]] stated in February 2013 that a "definitive" answer might require "another few years" after the [[Large Hadron Collider#Full operation|collider's 2015 restart]].<ref>{{cite news|last=Boyle|first=Alan|title=Will our universe end in a 'big slurp'? Higgs-like particle suggests it might|url=http://cosmiclog.nbcnews.com/_news/2013/02/18/17006552-will-our-universe-end-in-a-big-slurp-higgs-like-particle-suggests-it-might?lite|accessdate=20 February 2013|newspaper=NBCNews.com – cosmic log|date=2013-02-16|quote='it's going to take another few years' after the collider is restarted to confirm definitively that the newfound particle is the Higgs boson.}}</ref> In early March 2013, CERN Research Director Sergio Bertolucci stated that confirming spin-0 was the major remaining requirement to determine whether the particle is at least some kind of Higgs boson.<ref>{{cite web|last=Gillies|first=James|title=A question of spin for the new boson|url=http://home.web.cern.ch/about/updates/2013/03/question-spin-new-boson|publisher=[[CERN]]|accessdate=7 March 2013|date=2013-03-06}}</ref>
 
{{anchor|Current status}}<!--USED FOR INTERNAL LINKS-->
 
=== Confirmation of new particle as a Higgs boson, and current status ===
 
On 14 March 2013 CERN confirmed that:
:  "CMS and ATLAS have compared a number of options for the spin-parity of this particle, and these all prefer no spin and positive parity [two fundamental criteria of a Higgs boson consistent with the Standard Model]. This, coupled with the measured interactions of the new particle with other particles, strongly indicates that it is a Higgs boson."&nbsp;<ref name="CERN March 2013" />
This also makes the particle the first elementary [[scalar boson|scalar particle]] to be discovered in nature.<ref name="WSJ 14 March 2013" />
 
Examples of tests used to validate whether the 125 GeV particle is a Higgs boson:<ref name="strassler nov 2012" /><ref name="when higgs">{{cite web|last=Adam Falkowski (writing as 'Jester')|title=When shall we call it Higgs?|url=http://resonaances.blogspot.co.uk/2013/02/when-shall-we-call-it-higgs.html|publisher=Résonaances particle physics blog|accessdate=7 March 2013|date=2013-02-27}}</ref>
:{| class="wikitable" style="font-size:90%"
|-
! Requirement
! style="width:50%;"| How tested / explanation
! style="width:30%;"| Current status (March 2013)
|-
| Zero [[spin (physics)|spin]]|| Examining decay patterns. Spin-1 had been ruled out at the time of initial discovery by the observed decay to two {{nowrap|photons (γ γ),}} leaving spin-0 and spin-2 as remaining candidates.|| Spin-0 tentatively confirmed in March 2013.<ref name="CERN March 2013" />
|-
| <sup>+</sup> and not <sup>−</sup>&nbsp;[[parity (physics)|parity]] || Studying the angles at which decay products fly apart. Negative parity was also disfavoured if spin-0 was confirmed.<ref>{{cite web|title=Higgs-like Particle in a Mirror |url=http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.110.081803|accessdate=26 February 2013|publisher=American Physical Society}}</ref>|| Positive parity tentatively confirmed.<ref name="CERN March 2013" />
|-
| [[Particle decay|Decay channels]] (outcomes of particle decaying) are as predicted || The Standard Model predicts the decay patterns of a 125–126 GeV Higgs boson. Are these all being seen, and at the right rates?
 
Particularly significant, we should observe decays into pairs of {{nowrap|[[photon]]s (γ γ),}} [[W and Z bosons]] (WW and ZZ), [[bottom quark]]s (bb), and [[tau lepton]]s {{nowrap|(τ τ)}}, among the possible outcomes.
| {{nowrap|γ γ}}, WW and ZZ observed; {{nowrap|bb, τ τ}} not yet confirmed.<!--THERE MAY BE OTHER CHANNELS STUDIED, WITHOUT SOURCES WE CANNOT SAY THESE ARE THE ONLY CHANNELS THAT WILL BE STUDIED, THEY ARE JUST EXAMPLES FROM SOURCES --> Some branching levels (decay rates) are a little higher than expected in preliminary results,  in particular {{nowrap|H → γ γ}} which gives a peak at [[ATLAS]] a little higher than that seen in 4-lepton decays and at [[Compact Muon Solenoid|CMS]].<ref>{{cite web|last=Adam Falkowski (writing as 'Jester')|title=Twin Peaks in ATLAS|url=http://www.resonaances.blogspot.it/2012/12/twin-peaks-in-atlas.html|publisher=Résonaances particle physics blog|accessdate=24 February 2013|date=2012-12-13}}</ref>
|-
| [[Coupling (physics)|Couples to mass]]<br />(i.e., interacts with particles that have mass) || Particle physicist Adam Falkowski states that the essential qualities of a Higgs boson are that it is a spin-0 (scalar) particle which ''also'' couples to mass (W and Z bosons); proving spin-0 alone is insufficient.<ref name="when higgs" />
| Couplings to mass strongly evidenced ("At 95% confidence level c<sub>V</sub> is within 15% of the standard model value c<sub>V</sub>=1").<ref name="when higgs" />
|-
| Higher energy results remain consistent || After the [[Large Hadron Collider#Full operation|LHC's 2015 restart]] at the LHC's full planned energies of {{nowrap|13 – 14 TeV}}, searches for multiple Higgs particles (as predicted in some theories) and tests targeting other versions of particle theory will take place. These higher energy results must continue to give results consistent with Higgs theories || To be studied following LHC upgrade
|}
 
== Public discussion ==
 
=== Naming ===
 
==== Names used by physicists ====
The name most strongly associated with the particle and field is the Higgs boson<ref name="frank_close_infinity_puzzle" />{{rp|168}} and Higgs field. For some time the particle was known by a combination of its PRL author names (including at times Anderson), for example the Brout–Englert–Higgs particle, the Anderson-Higgs particle, or the Englert–Brout–Higgs–Guralnik–Hagen–Kibble mechanism,{{#tag:ref|Other names have included: the "Anderson–Higgs" mechanism,<ref>{{cite doi|10.1103/PhysRevB.65.132513|noedit}}</ref> "Higgs–Kibble" mechanism (by Abdus Salam)<ref name="frank_close_infinity_puzzle">{{cite book|last=Close|first=Frank|title=The Infinity Puzzle: Quantum Field Theory and the Hunt for an Orderly Universe|year=2011|publisher=Oxford University Press|location=Oxford|isbn=978-0-19-959350-7}}</ref> and "ABEGHHK'tH" mechanism [for Anderson, Brout, Englert, Guralnik, Hagen, Higgs, Kibble and 't Hooft] (by Peter Higgs).<ref name="frank_close_infinity_puzzle"/>|group=Note}} and these are still used at times.<ref name="scholarpedia" /><ref name="Nature-Higgs name" /> Fueled in part by the issue of recognition and a potential shared Nobel Prize,<ref name="Nature-Higgs name">{{cite journal|last=Editorial|title=Mass appeal: As physicists close in on the Higgs boson, they should resist calls to change its name|journal=Nature|date=2012-03-21|volume=483, 374|doi=10.1038/483374a|url=http://www.nature.com/nature/journal/v483/n7390/full/483374a.html|accessdate=21 January 2013|issue=7390|page=374|ref=harv|bibcode = 2012Natur.483..374. }}</ref><ref name="Nova">{{cite web|last=Becker|first=Kate|title=A Higgs by Any Other Name|url=http://www.pbs.org/wgbh/nova/physics/blog/2012/03/a-higgs-by-any-other-name|publisher="NOVA" (PBS) physics|accessdate=21 January 2013|date=2012-03-29}}</ref> the most appropriate name is still occasionally a topic of debate as at 2012.<ref name="Nature-Higgs name" /> (Higgs himself prefers to call the particle either by an acronym of all those involved, or "the scalar boson", or "the so-called Higgs particle".<ref name="Nova" />)
 
A considerable amount has been written on how Higgs' name came to be exclusively used. Two main explanations are offered.
<!--Please discuss changes first on the Talk page  -->
:{| class=wikitable style="font-size:90%"
|-
! Reason !! Basis of explanation
|-
| Higgs undertook a step which was either unique, clearer or more explicit in his paper, in formally predicting and examining the particle.
| Of the PRL papers' authors, only the paper by Higgs ''explicitly'' offered as a prediction, that a massive particle would exist, and calculated some of its properties;<ref name="frank_close_infinity_puzzle" />{{rp|167}}<ref name="CERNHiggsFAQ">{{cite web|url=http://cdsweb.cern.ch/journal/CERNBulletin/2012/28/News%20Articles/1459456?ln=en|title=Frequently Asked Questions: The Higgs!|work=The Bulletin|publisher=CERN|accessdate= 18 July 2012}}</ref> he was therefore "the first to postulate the existence of a massive particle" according to ''[[Nature (journal)|Nature]]''.<ref name="Nature-Higgs name" /> Physicist and author [[Frank Close]] and physicist-blogger [[Peter Woit]] both comment that the paper by GHK was also completed after Higgs and Brout–Englert were published.<ref name="frank_close_infinity_puzzle" />{{rp|167}}<ref name="woit2013">[http://www.math.columbia.edu/~woit/wordpress/?p=5753 Woit's physics blog ''"Not Even Wrong"'': Anderson on Anderson-Higgs] 2013-04-13</ref> and that Higgs alone had drawn attention to a predicted massive ''scalar'' boson, while all others had focused on the massive ''vector'' bosons;<ref name="frank_close_infinity_puzzle" />{{rp|154, 166, 175}}<ref name="woit2013" /> In this way, Higgs' contribution also provided experimentalists with a crucial "concrete target" needed to test the theory.<ref>{{cite news|last=Sample|first=Ian|title=Higgs boson's many great minds cause a Nobel prize headache|url=http://www.guardian.co.uk/science/2012/jul/04/higgs-boson-nobel-prize-headache|accessdate=23 July 2013|newspaper=The Guardian|date=2012-07-04|location=London}}</ref> However in Higgs' view, Brout and Englert did not explicitly mention the boson since its existence is plainly obvious in their work,<ref name="MyLifeAsABoson" />{{rp|6}} while according to Guralnik the GHK paper was a complete analysis of the entire symmetry breaking mechanism whose [[mathematical rigour]] is absent from the other two papers, and a massive particle may exist in some solutions.<ref name="Guralnik 2009" />{{rp|9}} Higgs' paper also provided an "especially sharp" statement of the challenge and its solution according to [[history of science|science historian]] David Kaiser.<ref name="Nova" />
|-
| The name was popularised in the 1970s due to its use as a convenient shorthand or because of a mistake in citing.
| Many accounts (including Higgs' own<ref name="MyLifeAsABoson" />{{rp|7}}) credit the "Higgs" name to physicist [[Benjamin W. Lee|Benjamin Lee]] (in [[Korean language|Korean]]: Lee Whi-soh). Lee was a significant populist for the theory in its early stages, and habitually attached the name "Higgs" as a "convenient shorthand" for its components from 1972<ref name="ISample29052009"/><ref name="Nature-Higgs name" /><ref>{{Cite press release|url=http://www.pas.rochester.edu/urpas/news/Hagen_030708|title=Rochester's Hagen Sakurai Prize Announcement|publisher=University of Rochester|year=2010}}</ref><ref>{{Cite video
  | title = C.R. Hagen Sakurai Prize Talk
  | url = http://www.youtube.com/watch?v=QrCPrwRBi7E&feature=PlayList&p=BDA16F52CA3C9B1D&playnext_from=PL&index=9
  | medium = YouTube
  | location =
  | date = 2010 }}
</ref><ref name="Peskin">{{cite web|last=Peskin|first=M.|title=40 Years of the Higgs Boson|url=http://www-conf.slac.stanford.edu/ssi/2012/Presentations/Peskin.pdf|work=Presentation at SSI 2012|publisher=Standford/SSI 2012|pages=3–5|accessdate=21 January 2013|date=July 2012|quote= quoting Lee's ICHEP 1972 presentation at Fermilab: "...which is known as the Higgs mechanism..." and "Lee's locution" – his footnoted explanation of this shorthand}}</ref> and in at least one instance from as early as 1966.{{#tag:ref|{{cite journal|journal=Science|date=2012-09-14|volume=337|page=1287|url=http://211.144.68.84:9998/91keshi/Public/File/41/337-6100/pdf/1287.full.pdf|accessdate=12 February 2013|quote=Lee ... apparently used the term 'Higgs Boson' as early as 1966... but what may have made the term stick is a seminal paper Steven Weinberg...published in 1967...Weinberg acknowledged the mix-up in an essay in the ''New York Review of Books'' in May 2012.|doi=10.1126/science.337.6100.1287|pmid=22984044|last1=Cho|first1=A|title=Particle physics. Why the 'Higgs'?|issue=6100|ref=harv}} (See also original article in ''[[New York Review of Books]]''<ref name="New York Review 2012">{{cite news|last=Weinberg|first=Steven|title=The Crisis of Big Science|url=http://www.nybooks.com/articles/archives/2012/may/10/crisis-big-science/?pagination=false|accessdate=12 February 2013|newspaper=[[The New York Review of Books]]|location=footnote 1|date=2012-05-10}}</ref> and Frank Close's 2011 book ''The Infinity Puzzle''<ref name="frank_close_infinity_puzzle" />{{rp|372}} ''([http://books.google.com/books?id=EDySwmXOEhMC&printsec=frontcover&dq=the+infinity+puzzle&hl=en&sa=X&ei=F9oaUc-NLYqe0QXCoYGIBQ&redir_esc=y#v=snippet&q=unintended%20consequence%20for%20history&f=false Book extract])'' which identified the error)|name=Lee_Weinberg_2012_name}}<ref name="frank_close_infinity_puzzle" />{{rp|167}} Although Lee clarified in his footnotes that "'Higgs' is an abbreviation for Higgs, Kibble, Guralnik, Hagen, Brout, Englert",<ref name="Peskin" /> his use of the term (and perhaps also Steven Weinberg's mistaken cite of Higgs' paper as the first in his seminal 1967 paper<ref name="frank_close_infinity_puzzle" /><ref name="New York Review 2012" /><ref name="Lee_Weinberg_2012_name" />) meant that by around 1975–76 others had also begun to use the name 'Higgs' exclusively as a shorthand.<ref>Examples of early papers using the term "Higgs boson" include 'A phenomenological profile of the Higgs boson' (Ellis, Gaillard and Nanopoulos, 1976), 'Weak interaction theory and neutral currents' (Bjorken, 1977), and 'Mass of the Higgs boson' (Wienberg, received 1975)</ref>
|}
 
==== Nickname ====
The Higgs boson is often referred to as the "God particle" in popular media outside the scientific community. The nickname comes from the title of [[The God Particle: If the Universe Is the Answer, What Is the Question?|a 1993 book on the Higgs boson and particle physics]] by [[Nobel Prize for Physics|Nobel Physics prizewinner]] and [[Fermilab]] director [[Leon Lederman]],<ref name="L&T">{{cite book| title = The God Particle: If the Universe is the Answer, What is the Question | year = 1993| publisher = Houghton Mifflin Company| author = Leon M. Lederman and Dick Teresi}}</ref> who wrote it in the context of failing US government support for the [[Superconducting Super Collider]],<ref name="SSC LA Times" /> a part-constructed titanic<ref>{{cite news|title=A Supercompetition For Illinois|url=http://articles.chicagotribune.com/1986-10-31/news/8603220012_1_illinois-electron-volts-high-energy|accessdate=16 January 2013|date=1986-10-31|quote=The SSC, proposed by the U.S. Department of Energy in 1983, is a mind-bending project ...  this gigantic laboratory ...  this titanic project|work=Chicago Tribune}}</ref><ref>{{cite news|last=Diaz|first=Jesus|title=This Is [The] World's Largest Super Collider That Never Was|url=http://gizmodo.com/5968784/this-is-worlds-largest-super-collider-that-never-was|accessdate=16 January 2013|newspaper=Gizmodo|date=2012-12-15|quote=...this titanic complex...}}</ref> competitor to the [[Large Hadron Collider]] with planned collision energies of {{nowrap|2 × 20 TeV}} that was championed by Lederman since its 1983 inception<ref name="SSC LA Times">{{cite news|last=ASCHENBACH|first=JOY|title=No Resurrection in Sight for Moribund Super Collider : Science: Global financial partnerships could be the only way to salvage such a project. But some feel that Congress delivered a fatal blow|url=http://articles.latimes.com/1993-12-05/news/mn-64100_1_superconducting-super-collider|accessdate=16 January 2013|newspaper=[[Los Angeles Times]]|date=1993-12-05|quote='We have to keep the momentum and optimism and start thinking about international collaboration,' said Leon M. Lederman, the Nobel Prize-winning physicist who was the architect of the super collider plan}}</ref><ref name="Illinois Issues 1987">{{cite news|last=Abbott|first=Charles|title=Illinois Issues journal, June 1987|url=http://www.lib.niu.edu/1987/ii8706tc.html|date=June 1987|page=18|quote=Lederman, who considers himself an unofficial propagandist for the super collider, said the SSC could reverse the physics brain drain in which bright young physicists have left America to work in Europe and elsewhere.}}</ref><ref name="Caltech">{{cite journal|last=Kevles|first=Dan|journal=[[California Institute of Technology]]: "Engineering & Science"|volume=58 no. 2|issue=Winter 1995|pages=16–25|url=http://calteches.library.caltech.edu/568/1/ES58.2.1995.pdf|title=Good-bye to the SSC: On the Life and Death of the Superconducting Super Collider|accessdate=16 January 2013|quote=Lederman, one of the principal spokesmen for the SSC, was an accomplished high-energy experimentalist who had made Nobel Prize-winning contributions to the development of the Standard Model during the 1960s (although the prize itself did not come until 1988). He was a fixture at congressional hearings on the collider, an unbridled advocate of its merits.|ref=harv}}</ref> and shut down in 1993; the book sought in part to promote awareness of the significance and need for such a project in the face of its possible loss of funding.<ref name="Calder 2005">{{cite book|last=Calder|first=Nigel|title=Magic Universe:A Grand Tour of Modern Science|year=2005|pages=369–370|url=http://books.google.com/?id=E4NfZ9FDcc8C&pg=PA370&lpg=PA370#v=onepage&q=title%20of%20a%20book&f=false|quote=The possibility that the next big machine would create the Higgs became a carrot to dangle in front of funding agencies and politicians. A prominent American physicist, Leon lederman ''[sic]'', advertised the Higgs as The God Particle in the title of a book published in 1993 ...Lederman was involved in a campaign to persuade the US government to continue funding the Superconducting Super Collider... the ink was not dry on Lederman's book before the US Congress decided to write off the billions of dollars already spent|isbn=9780191622359}}</ref>
 
While media use of this term may have contributed to wider awareness and interest,<ref>Alister McGrath, [http://www.telegraph.co.uk/science/8956938/Higgs-boson-the-particle-of-faith.html Higgs boson: the particle of faith], ''[[The Daily Telegraph]]'', Published 15 December 2011. Retrieved 15 December 2011.</ref> many scientists feel the name is inappropriate<ref name="ISample29052009">
{{cite news
|first=Ian
|last=Sample
|date=29 May 2009
|title=Anything but the God particle
|url=http://www.guardian.co.uk/science/blog/2009/may/29/why-call-it-the-god-particle-higgs-boson-cern-lhc
|publisher=The Guardian
|location=London
|accessdate=24 June 2009
}}</ref><ref name="NatPost">{{cite web|url=http://news.nationalpost.com/2011/12/14/the-higgs-boson-why-scientists-hate-that-you-call-it-the-god-particle/|title=The Higgs boson: Why scientists hate that you call it the 'God particle'|publisher=National Post|date=14 December 2011}}</ref><ref name="ISample03032009">
{{cite news
|first=Ian
|last=Sample
|date=3 March 2009
|title=Father of the God particle: Portrait of Peter Higgs unveiled
|url=http://www.guardian.co.uk/science/blog/2009/mar/02/god-particle-peter-higgs-portrait-lhc
|publisher=The Guardian
|location=London
|accessdate=24 June 2009
}}</ref> since it is sensational [[hyperbole]] and misleads readers;<ref name="nickname-telegraph">{{cite news|last=Chivers|first=Tom|title=How the 'God particle' got its name|url=http://blogs.telegraph.co.uk/news/tomchiversscience/100123765/how-the-god-particle-got-its-name/|accessdate=2012-12-03|newspaper=The Telegraph|date=2011-12-13|location=London}}</ref> the particle also has nothing to do with [[God]],<ref name="nickname-telegraph" /> leaves open numerous [[unanswered questions in physics|questions in fundamental physics]], and does not explain the ultimate [[origin of the universe]]. Higgs, an [[atheist]], was reported to be displeased and stated in a 2008 interview that he found it "embarrassing" because it was "the kind of misuse... which I think might offend some people".<ref name="nickname-telegraph" /><ref name="nickname-reuters">[http://www.reuters.com/article/scienceNews/idUSL0765287220080407?sp=true Key scientist sure "God particle" will be found soon] Reuters news story. 7 April 2008.</ref><ref name=NS>"[http://www.newscientist.com/channel/opinion/mg19926732.100-interview-the-man-behind-the-god-particle.html Interview: the man behind the 'God particle']", [[New Scientist]] 13 September 2008, pp. 44–5 (original interview in the Guardian: [http://www.guardian.co.uk/science/2008/jun/30/higgs.boson.cern Father of the 'God Particle'], June 30, 2008)</ref> Science writer Ian Sample stated in his 2010 book on the search that the nickname is "universally hate[d]" by physicists and perhaps the "worst derided" in the [[history of physics]], but that (according to Lederman) the publisher rejected all titles mentioning "Higgs" as unimaginative and too unknown.<ref>{{cite book|last=Sample|first=Ian|title=Massive: The Hunt for the God Particle|year=2010|pages=148–149 and 278–279|url=http://books.google.com/?id=GuhAP7YCcuoC&pg=PA148&lpg=PA148#v=onepage&f=false|isbn=9781905264957}}</ref>
 
Lederman begins with a review of the long human search for knowledge, and explains that his tongue-in-cheek title draws an analogy between the impact of the Higgs field on the fundamental symmetries at the [[Big Bang]], and the apparent chaos of structures, particles, forces and interactions that resulted and shaped our present universe, with the biblical story of [[Tower of Babel|Babel]] in which the primordial single language of early [[Book of Genesis|Genesis]] was [[confusion of tongues|fragmented into many disparate languages]] and cultures.<ref>{{cite news|last=Cole|first=K.|title=One Thing Is Perfectly Clear: Nothingness Is Perfect|url=http://articles.latimes.com/2000/dec/14/local/me-65457|accessdate=17 January 2013|newspaper=[[Los Angeles Times]]|date=2000-12-14|page='Science File'|quote=Consider the early universe–a state of pure, perfect nothingness; a formless fog of undifferentiated stuff ... 'perfect symmetry' ... What shattered this primordial perfection? One likely culprit is the so-called Higgs field ... Physicist Leon Lederman compares the way the Higgs operates to the biblical story of Babel [whose citizens] all spoke the same language ... Like God, says Lederman, the Higgs differentiated the perfect sameness, confusing everyone (physicists included) ... [Nobel Prizewinner Richard] [[Richard Feynman{{!}}Feynman]] wondered why the universe we live in was so obviously askew ... Perhaps, he speculated, total perfection would have been unacceptable to God. And so, just as God shattered the perfection of Babel, 'God made the laws only nearly symmetrical'}}</ref>
 
{{quote|Today ... we have the standard model, which reduces all of reality to a dozen or so particles and four forces.  ... It's a hard-won simplicity [...and...] remarkably accurate. But it is also incomplete and, in fact, internally inconsistent... This boson is so central to the state of physics today, so crucial to our final understanding of the structure of matter, yet so elusive, that I have given it a nickname: the God Particle. Why God Particle? Two reasons. One, the publisher wouldn't let us call it the Goddamn Particle, though that might be a more appropriate title, given its villainous nature and the expense it is causing. And two, there is a connection, of sorts, to [[Book of Genesis|another book]], a ''much'' older one...|Leon M. Lederman and Dick Teresi|''The God Particle: If the Universe is the Answer, What is the Question''<ref name="L&T"/> p. 22}}
 
Lederman whimsically asks whether the Higgs boson was added just to perplex and confound those seeking knowledge of the universe, and whether physicists will be confounded by it as recounted in that story, or ultimately surmount the challenge and understand "how beautiful is the universe [God has] made".<ref>Lederman, p.&nbsp;22 ''et seq'':
: "Something we cannot yet detect and which, one might say, has been put there to test and confuse us ... The issue is whether physicists will be confounded by this puzzle or whether, in contrast to the unhappy Babylonians, we will continue to build the tower and, as Einstein put it, 'know the mind of God'."
: "And the Lord said, Behold the people are un-confounding my confounding. And the Lord sighed and said, Go to, let us go down, and there give them the God Particle so that they may see how beautiful is the universe I have made".</ref>
 
==== Other proposals ====
A renaming competition by British newspaper ''[[The Guardian]]'' in 2009 resulted in their science correspondent choosing the name "the [[champagne bottle]] boson" as the best submission: "The bottom of a champagne bottle is in the shape of the [[Higgs potential]] and is often used as an illustration in physics lectures. So it's not an embarrassingly grandiose name, it is memorable, and [it] has some physics connection too."<ref>
{{cite news
|first=Ian
|last=Sample
|date=12 June 2009
|title=Higgs competition: Crack open the bubbly, the God particle is dead
|url=http://www.guardian.co.uk/science/blog/2009/jun/05/cern-lhc-god-particle-higgs-boson
|work=The Guardian
|location=London
|accessdate=4 May 2010
}}</ref>
The name ''Higgson'' was suggested as well, in an opinion piece in the [[Institute of Physics]]' online publication ''physicsworld.com''.<ref>
{{cite news
|first=Fraser
|last=Gordon
|date=5 July 2012
|title=Introducing the higgson
|url=http://physicsworld.com/cws/article/indepth/2012/jul/04/introducing-the-higgson
|work=physicsworld.com
|accessdate=25 August 2012
}}</ref>
 
=== Media explanations and analogies ===
There has been considerable public discussion of analogies and explanations for the Higgs particle and how the field creates mass,<ref>{{cite news|last=Wolchover|first=Natalie|title=Higgs Boson Explained: How 'God Particle' Gives Things Mass|url=http://www.huffingtonpost.com/2012/07/03/higgs-boson-explained-god-particle_n_1645732.html|accessdate=21 January 2013|newspaper=[[Huffington Post]]|date=2012-07-03}}</ref><ref>{{cite news|last=Oliver|first=Laura|title=Higgs boson: how would you explain it to a seven-year-old?|url=http://www.guardian.co.uk/science/2012/jul/04/higgs-boson-readers-explain|accessdate=21 January 2013|newspaper=[[The Guardian]]|date=2012-07-04|location=London}}</ref> including coverage of explanatory attempts in their own right and a competition in 1993 for the best popular explanation by then-UK Minister for Science [[William Waldegrave, Baron Waldegrave of North Hill|Sir William Waldegrave]]<ref>{{cite news|last=Zimmer|first=Ben|title=Higgs boson metaphors as clear as molasses|url=http://www.bostonglobe.com/ideas/2012/07/14/metaphors-and-higgs-boson/UjdsEySmG63XIAcNN7LNSO/story.html|accessdate=21 January 2013|newspaper=[[The Boston Globe]]|date=2012-07-15}}</ref> and articles in newspapers worldwide.
 
[[File:Light dispersion of a mercury-vapor lamp with a flint glass prism IPNr°0125.jpg|thumb|right|200px|Photograph of light passing through a [[dispersive prism]]: the rainbow effect arises because [[photon]]s are not all affected to the same degree by the dispersive material of the prism.]]
An educational collaboration involving an LHC physicist and a [http://teachers.web.cern.ch/teachers/ High School Teachers at CERN] educator suggests that [[Dispersion (optics)|dispersion of light]] – responsible for the [[rainbow]] and [[dispersive prism]] – is a useful analogy for the Higgs field's symmetry breaking and mass-causing effect.<ref>{{cite web|title=The Higgs particle: an analogy for Physics classroom (section)|url=http://www.lhc-closer.es/php/index.php?i=1&s=6&p=5&e=0|publisher=www.lhc-closer.es (a collaboration website of LHCb physicist Xabier Vidal and High School Teachers at CERN educator Ramon Manzano)|accessdate=2013-01-09}}</ref>
 
:{| class="wikitable" style="font-size:90%"
|-
| '''Symmetry breaking<br />in optics''' || In a vacuum, light of all colours (or [[photon]]s of all [[wavelength]]s) travels at [[speed of light|the same velocity]], a symmetrical situation. In some substances such as [[glass]], [[water]] or [[air]], this symmetry is broken ''(See: [[Photon#Photons in matter|Photons in matter]])''. The result is that light of different wavelengths appears to have [[variable speed of light|different velocities]] (as seen from outside).
|-
| '''{{nowrap|Symmetry breaking<br />in particle physics}}''' || In 'naive' gauge theories, gauge bosons and other fundamental particles are all massless – also a symmetrical situation. In the presence of the Higgs field this symmetry is broken. The result is that particles of different types will have different masses.
|}
 
Matt Strassler uses electric fields as an analogy:<ref>{{cite news|last=Flam|first=Faye|title=Finally – A Higgs Boson Story Anyone Can Understand|url=http://www.philly.com/philly/blogs/evolution/Finally---A-Higgs-Boson-Story-Anyone-Can-Understand.html|accessdate=21 January 2013|newspaper=[[The Philadelphia Inquirer]] (philly.com)|date=2012-07-12}}</ref>
{{quote|Some particles interact with the Higgs field while others don’t. Those particles that feel the Higgs field act as if they have mass. Something similar happens in an [[electric field]] – charged objects are pulled around and neutral objects can sail through unaffected. So you can think of the Higgs search as an attempt to make waves in the Higgs field ''[create Higgs bosons]'' to prove it’s really there.}}
 
A similar explanation was offered by ''[[The Guardian]]'':<ref>{{cite news|last=Sample|first=Ian|title=How will we know when the Higgs particle has been detected?|url=http://www.guardian.co.uk/science/2011/apr/28/higgs-boson-rumour-cern-lhc|accessdate=21 January 2013|newspaper=[[The Guardian]]|date=2011-04-28|location=London}}</ref>
{{quote|The Higgs boson is essentially a ripple in a field said to have emerged at the birth of the universe and to span the cosmos to this day ... The particle is crucial however: it is the [[smoking gun]], the evidence required to show the theory is right.}}
 
The Higgs field's effect on particles was famously described by physicist David Miller as akin to a room full of political party workers spread evenly throughout a room: the crowd gravitates to and slows down famous people but does not slow down others.{{#tag:ref |In Miller's analogy, the Higgs field is compared to political party workers spread evenly throughout a room. There will be some people (in Miller's example an anonymous person) who pass through the crowd with ease, paralleling the interaction between the field and particles that do not interact with it, such as massless photons. There will be other people (in Miller's example the British prime minister) who would find their progress being continually slowed by the swarm of admirers crowding around, paralleling the interaction for particles that do interact with the field and by doing so, acquire a finite mass.<ref name="Miller analogy">{{cite web
| url        = http://www.hep.ucl.ac.uk/~djm/higgsa.html
| title      = A quasi-political Explanation of the Higgs Boson; for Mr Waldegrave, UK Science Minister 1993
| first = David
| last = Miller
| accessdate = 10 July 2012
}}</ref><ref>{{cite news
  |author    = Kathryn Grim
  |title=Ten things you may not know about the Higgs boson
  |url=http://www.symmetrymagazine.org/cms/?pid=1000921
  |publisher  = Symmetry Magazine
  |accessdate = 10 July 2012 }}</ref>|group="Note"}} He also drew attention to well-known effects in [[solid state physics]] where an electron's effective mass can be much greater than usual in the presence of a crystal lattice.<ref name="Miller analogy" />
 
Analogies based on [[Drag (physics)|drag]] effects, including analogies of "[[syrup]]" or "[[molasses]]" are also well known, but can be somewhat misleading since they may be understood (incorrectly) as saying that the Higgs field simply resists some particles' motion but not others' – a simple resistive effect could also conflict with [[Newton's third law]].<ref>{{cite web|last=David Goldberg, Associate Professor of Physics, Drexel University|title=What's the Matter with the Higgs Boson?|url=http://io9.com/5690248/whats-the-matter-with-the-higgs-boson|publisher=io9.com "Ask a physicist"|accessdate=21 January 2013|date=2010-10-17}}</ref>
 
=== Recognition and awards ===
There has been considerable discussion of how to allocate the credit if the Higgs boson is proven, made more pointed as a [[Nobel Prize in Physics|Nobel prize]] had been expected, and the very wide basis of people entitled to consideration. These include a range of theoreticians who made the Higgs mechanism theory possible, the theoreticians of the 1964 PRL papers (including Higgs himself), the theoreticians who derived from these, a working electroweak theory and the Standard Model itself, and also the experimentalists at CERN and other institutions who made possible the proof of the Higgs field and boson in reality. The Nobel prize has a limit of 3 persons to share an award, and some possible winners are already prize holders for other work, or are deceased (the prize is only awarded to persons in their lifetime). Existing prizes for works relating to the Higgs field, boson, or mechanism include:
* Nobel Prize in Physics (1979) – [[Steven Weinberg|Weinberg]] and [[Abdus Salam|Salam]] (and a co-creator), ''for contributions to the theory of the unified weak and electromagnetic interaction between elementary particles''&nbsp;<ref>[http://www.nobelprize.org/nobel_prizes/physics/laureates/1979 The Nobel Prize in Physics 1979] – official Nobel Prize website.</ref>
* Nobel Prize in Physics (1999) – [[Gerard 't Hooft|'t Hooft]] and [[Tini Veltman|Veltman]], ''for elucidating the quantum structure of electroweak interactions in physics''&nbsp;<ref>[http://www.nobelprize.org/nobel_prizes/physics/laureates/1999 The Nobel Prize in Physics 1999] – official Nobel Prize website.</ref>
* Nobel Prize in Physics (2008) – [[Yoichiro Nambu|Nambu]] (shared), ''for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics''&nbsp;<ref name="nambu nobel" />
* [[Sakurai Prize|J. J. Sakurai Prize for Theoretical Particle Physics]] (2010) – Hagen, Englert, Guralnik, Higgs, Brout, and Kibble, ''for elucidation of the properties of spontaneous symmetry breaking in four-dimensional relativistic gauge theory and of the mechanism for the consistent generation of vector boson masses'' <ref name="sakuraiprize" /> (for the 1964 papers described [[#History|above]])
* [[Wolf Prize]] (2004) – Englert, Brout, and Higgs
* Nobel Prize in Physics (2013) - [[Peter Higgs]] and [[François Englert]], ''for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN's Large Hadron Collider''&nbsp;<ref>[http://www.nobelprize.org/nobel_prizes/physics/laureates/2013/] – official Nobel Prize website.</ref>
 
Additionally [[Physical Review Letters]]' 50-year review (2008) recognized the 1964 PRL papers and Weinberg's 1967 paper ''A model of Leptons'' (the most cited paper in particle physics, as of 2012) "milestone Letters".<ref name="PRL_50years" />
 
Following reported observation of the Higgs-like particle in July 2012, several [[Indian media]] outlets reported on the supposed neglect of credit to [[Indian people|Indian]] physicist [[Satyendra Nath Bose]] after whose work in the 1920s the class of particles "[[bosons]]" is named<ref name="AP-20120710">{{cite news |last=Daigle |first=Katy |title=India: Enough about Higgs, let's discuss the boson |url=http://apnews.excite.com/article/20120710/D9VU1DRG0.html |date=10 July 2012 |newspaper=[[AP News]] |accessdate=10 July 2012}}</ref><ref name="NYT-20120919">{{cite news |last=Bal |first=Hartosh Singh |title=The Bose in the Boson |url=http://latitude.blogs.nytimes.com/2012/09/19/indians-clamor-for-credit-for-the-bose-in-boson/ |date=19 September 2012 |publisher=New York Times |accessdate=21 September 2012 }}</ref> (although physicists have described Bose's connection to the discovery as tenuous).<ref name=outlook-in-bose>{{cite news|last=Alikhan|first=Anvar|title=The Spark In A Crowded Field|url=http://www.outlookindia.com/article.aspx?281539|accessdate=10 July 2012|newspaper=Outlook India|date=16 July 2012}}</ref>
 
== Technical aspects and mathematical formulation ==
{{see also|Standard Model (mathematical formulation)}}
In the Standard Model, the Higgs field is a four-component scalar field that forms a complex [[doublet (physics)|doublet]] of the [[weak isospin]] [[SU(2)]] symmetry:
:{{NumBlk|:|<math>
\phi=\frac{1}{\sqrt{2}}
\left(
\begin{array}{c}
\phi^1 + i\phi^2 \\ \phi^0+i\phi^3
\end{array}
\right)\;,
</math>|{{EquationRef|1}}}}
while the field has charge +1/2 under the [[weak hypercharge]] [[U(1)]] symmetry (in the convention where the electric charge, ''Q'', the [[weak isospin]], ''I<sub>3</sub>'', and the weak hypercharge, ''Y'', are related by ''Q = I<sub>3</sub> + Y'').<ref name="PeskinSchroederHiggs"/>
 
[[File:Mecanismo de Higgs PH.png|thumb|The potential for the Higgs field, plotted as function of <math>\phi^0</math> and <math>\phi^3</math>. It has a ''Mexican-hat'' or ''champagne-bottle profile'' at the ground.]]
 
The Higgs part of the Lagrangian is<ref name="PeskinSchroederHiggs"/>
:{{NumBlk|:|<math>\mathcal{L}_H = \left|\left(\partial_\mu -i g W_\mu^a \tau^a -i\frac{g'}{2} B_\mu\right)\phi\right|^2 + \mu^2 \phi^\dagger\phi-\lambda (\phi^\dagger\phi)^2,</math>|{{EquationRef|2}}}}
 
where <math>W_\mu^a</math> and <math>B_\mu</math> are the [[gauge boson]]s of the SU(2) and U(1) symmetries, <math>g</math> and <math>g'</math> their respective [[coupling constant]]s, <math>\tau^a=\sigma^a/2</math> (where <math>\sigma^a</math> are the [[Pauli matrices]]) a complete set generators of the SU(2) symmetry, and <math>\lambda>0</math> and <math>\mu^{2}>0</math>, so that the [[ground state]] breaks the SU(2) symmetry (see figure). The ground state of the Higgs field (the bottom of the potential) is degenerate with different ground states related to each other by a SU(2) gauge transformation. It is always possible to [[unitarity gauge|pick a gauge]] such that in the ground state <math>\phi^1=\phi^2=\phi^3=0</math>. The expectation value of <math>\phi^0</math> in the ground state (the [[vacuum expectation value]] or vev) is then <math>\langle\phi^0\rangle = v</math>, where <math>v = \tfrac{|\mu|}{\sqrt{\lambda}}</math>. The measured value of this parameter is ~{{val|246|u=GeV/c2}}.<ref name="PDGreview2012"/> It has units of mass, and is the only free parameter of the Standard Model that is not a dimensionless number. Quadratic terms in <math>W_{\mu}</math> and <math>B_{\mu}</math> arise, which give masses to the ''W'' and ''Z'' bosons:<ref name="PeskinSchroederHiggs">{{harvnb|Peskin|Schroeder|1995|loc=Chapter 20}}</ref>
:{{NumBlk|:|<math>M_W = \frac{v|g|}2,</math>|{{EquationRef|3}}}}
:{{NumBlk|:|<math>M_Z=\frac{v\sqrt{g^2+{g'}^2}}2,</math>|{{EquationRef|4}}}}
with their ratio determining the [[Weinberg angle]], <math>\cos \theta_W = \frac{M_W}{M_Z} = \frac{|g|}{\sqrt{g^2+{g'}^2}}</math>, and leave a massless U(1) [[photon]], <math>\gamma</math>.
 
The quarks and the leptons interact with the Higgs field through [[Yukawa interaction]] terms:
:{{NumBlk|:|<math>\begin{align}\mathcal{L}_{Y} =
&-\lambda_u^{ij}\frac{\phi^0-i\phi^3}{\sqrt{2}}\overline u_L^i  u_R^j
+\lambda_u^{ij}\frac{\phi^1-i\phi^2}{\sqrt{2}}\overline d_L^i  u_R^j\\
&-\lambda_d^{ij}\frac{\phi^0+i\phi^3}{\sqrt{2}}\overline d_L^i  d_R^j
-\lambda_d^{ij}\frac{\phi^1+i\phi^2}{\sqrt{2}}\overline u_L^i  d_R^j\\
&-\lambda_e^{ij}\frac{\phi^0+i\phi^3}{\sqrt{2}}\overline e_L^i  e_R^j
-\lambda_e^{ij}\frac{\phi^1+i\phi^2}{\sqrt{2}}\overline \nu_L^i  e_R^j
+ \textrm{h.c.},\end{align}</math>|{{EquationRef|5}}}}
where <math>(d,u,e,\nu)_{L,R}^i</math> are left-handed and right-handed quarks and leptons of the ''i''th [[generation (physics)|generation]], <math>\lambda_{u,d,e}^{ij}</math>are matrices of Yukawa couplings where h.c. denotes the hermitian conjugate terms. In the symmetry breaking ground state, only the terms containing <math>\phi^0</math> remain, giving rise to mass terms for the fermions. Rotating the quark and lepton fields to the basis where the matrices of Yukawa couplings are diagonal, one gets
:{{NumBlk|:|<math>\mathcal{L}_{m} = -m_u^i\overline u_L^i  u_R^i -m_d^i\overline d_L^i  d_R^i -m_e^i\overline e_L^i  e_R^i+ \textrm{h.c.},</math>|{{EquationRef|6}}}}
where the masses of the fermions are <math> m_{u,d,e}^i = \lambda_{u,d,e}^i v/\sqrt{2}</math>,  and <math> \lambda_{u,d,e}^i </math> denote the eigenvalues of the Yukawa matrices.<ref name="PeskinSchroederHiggs"/>
 
== See also ==
; Standard Model
{{Wikipedia books|Particles of the Standard Model}}
* [[Quantum gauge theory]]
* [[Introduction to quantum mechanics]]
* [[Noncommutative standard model]] and [[noncommutative geometry]] generally
* [[Standard Model (mathematical formulation)]] (and especially [[Standard Model (mathematical formulation)#Quantum Field Theory|Standard Model fields overview]] and [[Standard Model (mathematical formulation)#Mass terms and the Higgs mechanism|mass terms and the Higgs mechanism]])
 
;Other
* [[Bose–Einstein statistics]]
* [[Dalitz plot]]
* [[Higgs boson in fiction]]
* [[Quantum triviality]]
* [[ZZ diboson]]
* [[Scalar boson]]
* [[Stueckelberg action]]
 
== Notes ==
{{reflist|group="Note"|30em}}
 
== References ==
{{Reflist|30em}}
 
== Further reading ==
{{Refbegin|30em}}
* {{cite book
|author=G.S. Guralnik, C.R. Hagen and T.W.B. Kibble
|year=1968
|chapter=Broken Symmetries and the Goldstone Theorem
|url=http://www.datafilehost.com/download-7d512618.html
|title=Advances in Physics, Vol. 2
|pages=567–708
|editor=R.L. Cool and R.E. Marshak
|publisher=[[Interscience Publishers]]
|isbn=978-0470170571
}}
* {{Cite journal |author=P. Higgs |title=Broken Symmetries, Massless Particles and Gauge Fields |journal=[[Physics Letters]] |year=1964 |volume=12 |issue=2 |page=132 |doi=10.1016/0031-9163(64)91136-9|bibcode = 1964PhL....12..132H |ref=harv }}
* {{Cite journal |author=Y. Nambu and G. Jona-Lasinio |title=Dynamical Model of Elementary Particles Based on an Analogy with Superconductivity |journal=[[Physical Review]] |year=1961 |volume=122 |pages=345–358 |doi=10.1103/PhysRev.122.345|bibcode = 1961PhRv..122..345N |ref=harv }}
* {{Cite journal |author=P.W. Anderson |title=Plasmons, Gauge Invariance, and Mass |journal=Physical Review |year=1963 |volume=130 |page=439 |doi=10.1103/PhysRev.130.439|bibcode = 1963PhRv..130..439A |ref=harv }}
* {{Cite journal |author=A. Klein and B.W. Lee |title=Does Spontaneous Breakdown of Symmetry Imply Zero-Mass Particles? |journal=[[Physical Review Letters]] |year=1964 |volume=12 |issue=10 |page=266 |doi=10.1103/PhysRevLett.12.266 |bibcode=1964PhRvL..12..266K |ref=harv}}
* {{Cite journal |author=W. Gilbert |title=Broken Symmetries and Massless Particles |journal=[[Physical Review Letters]] |year=1964 |volume=12 |issue=25 |page=713 |doi=10.1103/PhysRevLett.12.713 |bibcode=1964PhRvL..12..713G |ref=harv}}
{{Refend}}
 
== External links ==
{{Commons category}}
{{Wiktionary}}
 
=== Popular science, mass media, and general coverage ===
* [http://cms.web.cern.ch/news/about-higgs-boson Hunting the Higgs boson at C.M.S. Experiment, at CERN]
* [http://www.exploratorium.edu/origins/cern/ideas/higgs.html The Higgs boson]" by the CERN exploratorium.
* [http://theatomsmashers.com/ The Atom Smashers, a documentary film about the search for the Higgs boson at Fermilab.]
* [http://www.guardian.co.uk/science/higgs-boson Collected Articles at the ''Guardian'']
* [http://www.youtube.com/watch?v=vXZ-yzwlwMw Video (04:38)]&nbsp;– [[CERN]] Announcement on 4 July 2012, of the discovery of a particle which is suspected will be a Higgs boson.
* [http://vimeo.com/41038445 Video1 (07:44)] + [http://www.youtube.com/watch?v=0hn0jYjijNs Video2 (07:44)]&nbsp;– Higgs Boson Explained by [[CERN|CERN Physicist]], [http://www.faculty.uci.edu/profile.cfm?faculty_id=5436 Dr. Daniel Whiteson] (16 June 2011).
* [http://science.howstuffworks.com/higgs-boson.htm HowStuffWorks: What exactly is the Higgs boson?]
* {{cite web|last=Carroll|first=Sean|authorlink=Sean M. Carroll|title=Higgs Boson with Sean Carroll|url=http://www.sixtysymbols.com/videos/higgs_sean.htm|work=Sixty Symbols|publisher=University of Nottingham}}
* {{cite news|last=Overbye|first=Dennis|title=Chasing the Higgs Boson: How 2 teams of rivals at CERN searched for physics' most elusive particle|url=http://www.nytimes.com/2013/03/05/science/chasing-the-higgs-boson-how-2-teams-of-rivals-at-CERN-searched-for-physics-most-elusive-particle.html|accessdate=22 July 2013|newspaper=[[New York Times]] Science pages|date=2013-03-05}} - New York Times "behind the scenes" style article on the Higgs' search at ATLAS and CMS
* The story of the Higgs theory by the authors of the PRL papers and others closely associated:
** {{cite web|last=Higgs|first=Peter|title=My Life as a Boson|url=http://www.kcl.ac.uk/nms/depts/physics/news/events/MyLifeasaBoson.pdf|publisher=Talk given at Kings College, London, Nov 24 2010|year=2010|accessdate=17 January 2013}} (also: [http://www.worldscientific.com/doi/abs/10.1142/S0217751X02013046|date=2010-11-24])
** {{cite web|last=Kibble|first=Tom|title=Englert–Brout–Higgs–Guralnik–Hagen–Kibble mechanism (history)|url=http://www.scholarpedia.org/w/index.php?title=Englert–Brout–Higgs–Guralnik–Hagen–Kibble_mechanism_(history)&oldid=124215|publisher=Scholarpedia|accessdate=17 January 2013|year=2009}} (also: [http://dx.doi.org/10.4249/scholarpedia.8741])
** {{Cite journal | first=Gerald| last=Guralnik | title=The History of the Guralnik, Hagen and Kibble development of the Theory of Spontaneous Symmetry Breaking and Gauge Particles | journal=[[International Journal of Modern Physics A]] | year=2009 | volume=24 | issue=14 | pages=2601–2627 | arxiv=0907.3466| ref=harv | bibcode=2009IJMPA..24.2601G | doi=10.1142/S0217751X09045431 }}, {{cite arXiv |first=Gerald| last=Guralnik |title=The Beginnings of Spontaneous Symmetry Breaking in Particle Physics. Proceedings of the DPF-2011 Conference, Providence, RI, 8–13 August 2011 |year=2011|eprint=1110.2253v1 |class=physics.hist-ph}}, and Guralnik, Gerald (2013). [http://www.sps.ch/en/articles/milestones_in_physics/heretical_ideas_that_provided_the_cornerstone_for_the_standard_model_of_particle_physics_1/ "Heretical Ideas that Provided the Cornerstone for the Standard Model of Particle Physics".] SPG MITTEILUNGEN March 2013, No. 39, (p.&nbsp;14), and [http://www.youtube.com/watch?v=WLZ78gwWQI0 Talk at Brown University about the 1964 PRL papers]
** [http://www.conferences.uiuc.edu/bcs50/PDF/Anderson.pdf Philip Anderson (not one of the PRL authors) on symmetry breaking in superconductivity and its migration into particle physics and the PRL papers]
* [http://xkcd.com/812/ Cartoon about the search]
 
=== Significant papers and other ===
* [http://www.sciencedirect.com/science/article/pii/S037026931200857X Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC]
* [http://www.sciencedirect.com/science/article/pii/S0370269312008581 Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC]
* [http://pdg.lbl.gov/2012/listings/rpp2012-list-higgs-boson.pdf Particle Data Group: Review of searches for Higgs bosons.]
* [http://books.google.com/?id=ONhnbpq00xIC&pg=PA86 2001, a spacetime odyssey: proceedings of the Inaugural Conference of the Michigan Center for Theoretical Physics : Michigan, USA, 21–25 May 2001, (p.86&nbsp;– 88)], ed. Michael J. Duff, James T. Liu, ISBN 978-981-238-231-3, containing Higgs' story of the Higgs boson.
* A.A. Migdal & A.M. Polyakov, ''Spontaneous Breakdown of Strong Interaction Symmetry and the Absence of Massless Particles'',  Sov.J.-JETP 24,91 (1966) - example of a 1966 Russian paper on the subject.
 
=== Introductions to the field ===
* [http://www.calstatela.edu/faculty/kaniol/p544/rmp46_p7_higgs_goldstone.pdf Spontaneous symmetry breaking, gauge theories, the Higgs mechanism and all that (Bernstein, ''Reviews of Modern Physics'' Jan 1974)] - an introduction of 47 pages covering the development, history and mathematics of Higgs theories from around 1950 to 1974.
 
{{particles}}
{{Breakthrough of the Year}}
{{Use dmy dates|date=November 2012}}
{{Use British English|date=July 2012}}
 
[[Category:Bosons]]
[[Category:Electroweak theory]]
[[Category:Hypothetical elementary particles]]
[[Category:Mass]]
[[Category:Particle physics]]
[[Category:Phase transitions]]
[[Category:Standard Model]]
[[Category:Quantum field theory]]
 
{{Link GA|zh}}

Latest revision as of 14:48, 8 April 2014

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