# Neutral current

Jump to navigation Jump to search

Weak neutral current interactions are one of the ways in which subatomic particles can interact by means of the weak force. These interactions are mediated by the Template:SubatomicParticle boson. The discovery of weak neutral currents was a significant step toward the unification of electromagnetism and the weak force into the electroweak force, and led to the discovery of the W and Z bosons.

## Definition

The neutral current that gives the interaction its name is that of the interacting particles. For example, the neutral-current contribution to the Template:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticle elastic scattering amplitude

${\displaystyle {\mathfrak {M}}^{\mathrm {NC} }\propto J_{\mu }^{\mathrm {(NC)} }(\nu _{\mathrm {e} })\;J^{{\mathrm {(NC)} }\mu }({\mathrm {e^{-}} })}$

where the neutral currents describing the flow of the neutrino and of the electron are given by

${\displaystyle J^{{\mathrm {(NC)} }\mu }(f)={\bar {u}}_{f}\gamma ^{\mu }{\frac {1}{2}}\left(g_{V}^{f}-g_{A}^{f}\gamma ^{5}\right)u_{f},}$

The Template:SubatomicParticle boson can couple to any Standard Model particle, except gluons and photons. However, any interaction between two charged particles that can occur via the exchange of a virtual Template:SubatomicParticle boson can also occur via the exchange of a virtual photon. Unless the interacting particles have energies on the order of the Template:SubatomicParticle boson mass (91 GeV) or higher, the virtual Template:SubatomicParticle boson exchange has an effect of a tiny correction ( ${\displaystyle ~(E/M_{Z})^{2}}$ ) to the amplitude of the electromagnetic process. Particle accelerators with energies necessary to observe neutral current interactions and to measure the mass of Template:SubatomicParticle boson weren't available until 1983.

On the other hand, Template:SubatomicParticle boson interactions involving neutrinos have distinctive signatures: They provide the only known mechanism for elastic scattering of neutrinos in matter; neutrinos are almost as likely to scatter elastically (via Template:SubatomicParticle boson exchange) as inelastically (via Template:SubatomicParticle boson exchange). Weak neutral currents were predicted in 1973 by Abdus Salam, Sheldon Glashow and Steven Weinberg,[1] and confirmed shortly thereafter in 1973, in a neutrino experiment in the Gargamelle bubble chamber at CERN.