# Charged current

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{{Short description|One way that particles can interact with the weak force}}
{{see also|Mathematical formulation of the Standard Model}}
{{Standard model of particle physics|Electroweak interaction}}
'''Charged current''' interactions (as opposed to [neutral current](/source/neutral_current) interactions) are one of two primary channels in which subatomic particles can interact by means of the [weak force](/source/weak_force). These interactions are specifically mediated by the [{{SubatomicParticle|W boson+}} and {{SubatomicParticle|W boson-}} bosons](/source/W_and_Z_bosons).

== Overview ==
[[File:Beta Negative Decay.svg|thumb|right|280px|The simplest [Feynman diagram](/source/Feynman_diagram) for [beta decay](/source/beta_decay). It contains a charged current interaction at each vertex.]]

Charged current interactions are the most easily detected class of weak interactions. The weak force is best known for mediating [nuclear decay](/source/nuclear_decay). It has very short range, but is the only force (apart from [gravity](/source/gravity)) to interact with [neutrinos](/source/neutrinos). The weak force is communicated via the W and Z [exchange particles](/source/boson). Of these, the W-boson has either a positive or negative [electric charge](/source/electric_charge), and mediates neutrino absorption and emission by or with an electrically charged particle. During these processes, the W-boson induces electron or [positron emission](/source/positron_emission) or absorption, or changing the flavour of a quark as well as its electrical charge, such as in [beta decay](/source/beta_decay) or [K-capture](/source/K-capture).<ref>{{cite web|url=https://www2.ph.ed.ac.uk/~vjm/Lectures/ParticlePhysics2010_files/Particle8-23Nov.pdf|title=Particle Physics Handout 8|access-date=May 19, 2021|publisher=University of Edinburgh}}</ref>

By contrast, the Z particle is electrically neutral, and exchange of a [Z-boson](/source/Z-boson) leaves the interacting particles' quantum numbers unaffected, except for a transfer of momentum, spin, and energy.

Because exchange of W bosons involves a transfer of electric charge (as well as a transfer of [weak isospin](/source/weak_isospin), while [weak hypercharge](/source/weak_hypercharge) is not transferred), it is known as "charged current". By contrast, exchanges of Z bosons involve no transfer of electrical charge, so it is referred to as a "[neutral current](/source/neutral_current)". In the latter case, the word "current" has nothing to do with electricity &ndash; it simply refers to the Z bosons' movement between other particles.

== Definition ==
The name "charged current" arises due to currents of fermions coupled to the W bosons having electric charge. For example, the charged current contribution to the {{SubatomicParticle|Electron neutrino}}{{SubatomicParticle|Electron}} → {{SubatomicParticle|Electron neutrino}}{{SubatomicParticle|Electron}} elastic [scattering amplitude](/source/scattering_amplitude) is:<ref name=sm-cc-I>{{cite web|url=https://www.hep.ucl.ac.uk/~campanel/Post_Grads/2016-2017/SM-CC-Weak-Interactions-I.pdf|title=Charged Current weak interactions I|date=2016–2017|access-date=May 7, 2021|first=Keith|last=Hamilton|publisher=University College London|pages=16}}</ref>
:<math>\mathfrak{M}^{\mathrm{CC}} \propto J_{\mu}^{\mathrm{(CC)}}(\mathrm{e^{-}}\to\nu_{\mathrm{e}}) \; J^{\mathrm{(CC)}\mu}(\nu_{\mathrm{e}}\to\mathrm{e^{-}}),</math>
where the charged currents describing the flow of one [fermion](/source/fermion) into the other are given by:<ref name=sm-cc-I/>
:<math>J^{\mathrm{(CC)\mu}}(f\to f') = \bar{u}_{f'}\gamma^{\mu}\frac{1}{2}\left(1-\gamma^{5}\right)u_{f}.</math>

The W-Boson can couple to any particle with [weak isospin](/source/weak_isospin) (i.e. any [left-handed](/source/Chirality_(physics)) [Standard Model](/source/Standard_Model) fermions).<ref group=Note>The W boson can also couple with any [electroweak](/source/electroweak) [gauge boson](/source/gauge_boson) and the [Higgs boson](/source/Higgs_boson), but these are typically not characterized as charged current interactions.</ref>

==See also==
* [Neutral current](/source/Neutral_current)
* [W and Z bosons](/source/W_and_Z_bosons)

==Notes==
<references group=Note/>

==References==
{{reflist}}

Category:Electroweak theory

{{Particle-stub}}

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Adapted from the Wikipedia article [Charged current](https://en.wikipedia.org/wiki/Charged_current) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Charged_current?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.