Weakneutral current interactions are one of the ways in whichsubatomic particles can interact by means of theweak force. These interactions are mediated by theZ boson. The discovery of weak neutral currents was a significant step toward the unification ofelectromagnetism and the weak force into theelectroweak force, and led to the discovery of theW and Z bosons.

The weak force is best known for its role in nuclear decay. It has very short range but (apart from gravity) is the only force to interact withneutrinos. Like other subatomic forces, the weak force is mediated via exchange particles. Perhaps the most well known of the exchange particles for the weak force is theW particle which is involved inbeta decay. W particles haveelectric charge – there are both positive and negative W particles – however the Z boson is also an exchange particle for the weak force but doesnot have any electrical charge.

Exchange of a Z boson transfersmomentum,spin, andenergy, but leaves the interacting particles' quantum numbers unaffected – charge,flavor,baryon number,lepton number, etc. Because there is no transfer of electrical charge involved, exchange of Z particles is referred to as "neutral" in the phrase "neutral current". However the word "current" here has nothing to do with electricity – it simply refers to the exchange of the Z particle.^[1]

The Z boson's neutral current interaction is determined by a derived quantum number calledweak charge, which acts similarly toweak isospin for interactions with the W bosons.

The neutral current that gives the interaction its name is that of the interacting particles.

For example, the neutral current contribution to theν
_ee⁻
→ν
_ee⁻
elasticscattering amplitude is

${\displaystyle {\mathfrak{M}}^{\mathsf{N}\mathsf{C}}\propto J_{\mu }^{\mathsf{(}\mathsf{N}\mathsf{C}\mathsf{)}}({\nu }_{\mathrm{e}})J^{\mathsf{(}\mathsf{N}\mathsf{C}\mathsf{)}\mu }({\mathrm{e}}^{-}),}$

where the neutral currents describing the flow of theneutrino and of the electron are given by:^[2]

${\displaystyle J^{\mathsf{(}\mathsf{N}\mathsf{C}\mathsf{)}\mu }(f)={\overline{u}}_f{\gamma }^{\mu }\frac{1}{2}\left(g_{\mathsf{V}}^f-g_{\mathsf{A}}^f{\gamma }^5\right)u_f,}$

where:^[2]

${\displaystyle g_{\mathsf{V}}^f=T_3(f)-2{\sin }^2{\theta }_{\mathsf{W}}Q(f)=\frac{1}{2}{Q}_{\mathsf{W}}(f)}$

and${\displaystyle g_{\mathsf{A}}^f=T_3(f)}$ are thevector and axial couplings forfermion${\displaystyle f.}$${\displaystyle T_3}$ denotes theweak isospin of the fermions,Q their electric charge and${\displaystyle Q_{\mathsf{W}}}$ theirweak charge. Thesecouplings amount to essentially left chiral for neutrinos and axial for charged leptons.

The Z boson can couple to anyStandard Model particle, exceptgluons andphotons (sterile neutrinos would also be an exception, if they were found to exist). However, any interaction between two charged particles that can occur via the exchange of a virtual Z boson can also occur via the exchange of a virtualphoton. Unless the interacting particles have energies on the order of the Z boson mass (91 GeV) or higher, the virtual Z boson exchange has an effect of a tiny correction,${\displaystyle (E/M_{\mathrm{Z}}{)}^2,}$ to the amplitude of the electromagnetic process.

Particle accelerators with energies necessary to observe neutral current interactions and to measure the mass of Z boson weren't available until 1983.

On the other hand, Z boson interactions involvingneutrinos have distinctive signatures: They provide the only known mechanism forelastic scattering of neutrinos in matter. Neutrinos are almost as likely to scatter elastically (via Z boson exchange) as inelastically (viaW boson exchange); this effect has considerable significance for neutrino observational experiments, e.g. in theSudbury Neutrino Observatory experiment.

Weak neutral currents were predicted byelectroweak theory developed mainly byAbdus Salam,John Clive Ward,Sheldon Glashow andSteven Weinberg,^[3] and confirmed shortly thereafter in 1973, in a neutrino experiment in theGargamellebubble chamber atCERN.

• Charged current
• Flavor changing neutral current
• Neutral particle oscillation
• Electric current
• Quantum chromodynamics
• Sudbury Neutrino Observatory#Neutral current interaction
• Weak charge

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• "Neutral current interaction".Britannica.
• Nave, R."Neutral current". GSU.
• Nieves, J.; Valverde, M.; Vicente Vacas, M.J. (2006)."Charged and neutral current neutrino induced nucleon emission reactions"(PDF).Acta Physica Polonica B.37 (8):2295–2301.arXiv:hep-ph/0605221.Bibcode:2006AcPPB..37.2295N. Archived fromthe original(PDF) on 21 January 2012.
• "Gargamelle".Symmetry Magazine. 2009-07-07.
• Fraser, Gordon (3 November 1998)."Twenty-five years of neutral currents".CERN Courier. 27904. Archived fromthe original on 13 November 2011. Retrieved27 August 2011.Gordon Fraser looks back at how confirmation of the existence of neutral currents ushered in a new understanding of physics.
• Fenkart, Sanje (3 July 2023)."CERN's neutrino odyssey".CERN Courier.Sanje Fenkart reounts the discovery of neutral currents in its 50 years anniversary
• Padilla, Antonio (Tony).Brady Haran (ed.)."Gargamelle and neutral currents".Sixty Symbols.University of Nottingham.

• Electroweak theory

• Articles with short description
• Short description matches Wikidata