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Weak '''neutral current''' interactions are one of the ways in which [[subatomic particle]]s can interact by means of the [[weak force]]. These interactions are mediated by the {{SubatomicParticle|link=yes|Z boson}} [[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 {{SubatomicParticle|Electron neutrino}}{{SubatomicParticle|Electron}} → {{SubatomicParticle|Electron neutrino}}{{SubatomicParticle|Electron}} elastic scattering amplitude
:<math>\mathfrak{M}^{\mathrm{NC}} \propto J_{\mu}^{\mathrm{(NC)}}(\nu_{\mathrm{e}}) \; J^{\mathrm{(NC)}\mu}(\mathrm{e^{-}})</math>
where the neutral currents describing the flow of the neutrino and of the electron are given by
:<math>J^{\mathrm{(NC)}\mu}(f) = \bar{u}_{f}\gamma^{\mu}\frac{1}{2}\left(g^{f}_{V}-g^{f}_{A}\gamma^{5}\right)u_{f},</math>
and <math>g^{f}_{V}</math> and <math>g^{f}_{A}</math> are the [[Coordinate vector|vector]] and [[axial vector]] couplings for [[fermion]] <math>f</math>.

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

On the other hand, {{SubatomicParticle|Z boson}} boson interactions involving [[neutrino]]s 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 {{SubatomicParticle|Z boson}} boson exchange) as inelastically (via {{SubatomicParticle|link=yes|W boson}} boson exchange). Weak neutral currents were predicted in 1973 by [[Abdus Salam]], [[Sheldon Glashow]] and [[Steven Weinberg]],<ref>{{cite web|title=The Nobel Prize in Physics 1979|url=http://www.nobel.se/physics/laureates/1979|publisher=[[Nobel Foundation]]|accessdate=2008-09-10}}</ref> and confirmed shortly thereafter in 1974, in a neutrino experiment in the [[Gargamelle]] [[bubble chamber]] at [[CERN]].

== See also ==
* [[Charged current]]
* [[Flavor changing neutral current]]
* [[Quantum chromodynamics]]

== References ==
{{Reflist}}

== External links ==
* [http://cerncourier.com/cws/article/cern/29168 ''THE DISCOVERY OF WEAK NEUTRAL CURRENTS'', CERN Courier]
* [http://public.web.cern.ch/public/en/Research/Gargamelle-en.html public web CERN]
* [http://www.britannica.com/EBchecked/topic/410842/neutral-current-interaction britannica]
* [http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neucur.html R Nave]
* http://www.actaphys.uj.edu.pl/vol37/pdf/v37p2295.pdf
* http://www.symmetrymagazine.org/breaking/2009/07/07/gargamelle/
* [http://cerncourier.com/cws/article/cern/27904 cerncourier]
* {{cite web|last=Padilla|first=Antonio (Tony)|title=Gargamelle and Neutral Currents|url=http://www.sixtysymbols.com/videos/neutral_currents.htm|work=Sixty Symbols|publisher=[[Brady Haran]] for the [[University of Nottingham]]}}

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[[Category:Particle physics]]

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