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2012-01-01T08:19:26Z

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{{Infobox software
| name = NNPDF
| logo = [[Image:LogoNNPDF.png|250px|NNPDF Logo]]
| developer = The NNPDF Collaboration
| working_state = Current
| source_model = [[Open source]]
| latest_release_version = 2.3
| status = Active
| genre = [[Particle Physics]]
| website = {{URL|http://nnpdf.hepforge.org}}
}}

'''NNPDF''' is used to denote the [[parton distribution functions]] from the NNPDF Collaboration which is based on a
combination of a [[Monte Carlo]] method for experimental data sampling with the use of [[neural networks]] as basic interpolating functions.

== The NNPDF approach ==
[[File:General-strategy-evol.jpg|thumb|300px|The NNPDF Collaboration strategy is summarized in this diagram.]]
The NNPDF approach can be divided into four main steps:
* The generation of a large sample of Monte Carlo replicas of the original experimental data, in a way that central values, errors and correlations are reproduced with enough accuracy.
* The training (minimization of the <math>\chi^2</math>) of a set of PDFs parametrized by [[artificial neural network|neural network]]s on each of the above MC replicas of the data. PDFs are parametrized at the initial evolution scale <math>Q^{2}_{0}</math> and then evolved to the experimental data scale <math>Q^2</math> by means of the [[DGLAP]] equations. Since the PDF parametrization is redundant, the minimization strategy is based in [[genetic algorithm]]s.
* The neural network training is stopped dynamically before entering into the overlearning regime, that is, so that the PDFs learn the physical laws which underlie experimental data without fitting simultaneously statistical noise.
* Once the training of the MC replicas has been completed, a set of statistical estimators can be applied to the set of PDFs, in order to assess the statistical consistency of our results. For example, the stability with respect PDF parametrization can be explicitly verified.

The set of <math>N_{rep}</math> PDF sets (trained neural networks) provides a representation of the underlying PDF probability density, from which any statistical estimator can be computed.

== Examples of PDF plots ==

The image below shows the [[gluon]] at small-x from the [http://arxiv.org/abs/0808.1231 the NNPDF1.0 analysis], available
through [http://projects.hepforge.org/lhapdf/ the LHAPDF interface]

<gallery widths=444px heights=300px>
File:Gluon log ref.jpg|The NNPDF1.0 gluon
</gallery>

== NNPDF Parton Distributions releases ==
The NNPDF releases are summarised in the following table:
{| class="wikitable centered sortable" style="text-align: center;"
|-
! PDF set
! DIS data
! Drell-Yan data
! Jet data
! LHC data
! Independent param. of <math>s</math> and <math>\bar{s}</math>
! Heavy Quark masses
! NNLO
|-
| [http://projects.hepforge.org/lhapdf/ '''NNPDF2.2''']
| style="background: lightgreen;"| yes
| style="background: lightgreen;"| yes
| style="background: lightgreen;"| yes
| style="background: lightgreen;"| yes
| style="background: lightgreen;"| yes
| style="background: lightgreen;"| yes
| style="background: lightgreen;"| yes
|-
| [http://projects.hepforge.org/lhapdf/ '''NNPDF2.1''']
| style="background: lightgreen;"| yes
| style="background: lightgreen;"| yes
| style="background: lightgreen;"| yes
| style="background: pink;"| no
| style="background: lightgreen;"| yes
| style="background: lightgreen;"| yes
| style="background: lightgreen;"| yes
|-
| [http://projects.hepforge.org/lhapdf/ '''NNPDF2.0''']
| style="background: lightgreen;"| yes
| style="background: lightgreen;"| yes
| style="background: lightgreen;"| yes
| style="background: pink;"| no
| style="background: lightgreen;"| yes
| style="background: pink;"| no
| style="background: pink;"| no
|-
| [http://projects.hepforge.org/lhapdf/ '''NNPDF1.2''']
| style="background: lightgreen;"| yes
| style="background: pink;"| no
| style="background: pink;"| no
| style="background: pink;"| no
| style="background: lightgreen;"| yes
| style="background: pink;"| no
| style="background: pink;"| no
|-
| [http://projects.hepforge.org/lhapdf/ '''NNPDF1.0''']
| style="background: lightgreen;"| yes
| style="background: pink;"| no
| style="background: pink;"| no
| style="background: pink;"| no
| style="background: pink;"| no
| style="background: pink;"| no
| style="background: pink;"| no
|-
|}

All PDF sets are available through the LHAPDF interface.

==External links==
*[http://nnpdf.hepforge.org The NNPDF Collaboration homepage]
*[http://sophia.ecm.ub.es/nnpdf/nnpdf-driver.htm Download NNPDF Parton Distribution sets]
*[http://arxiv.org/abs/0808.1231 The NNPDF1.0 analysis]
*[http://arxiv.org/abs/hep-ph/0701127 The NNPDF Non-Singlet analysis]
*[http://projects.hepforge.org/lhapdf/ The LHAPDF interface]

[[Category:Particle physics]]
[[Category:Physics software]]

Stably free module - Revision history

en>Qetuth: more specific stub type