neutralcurrent

Neutral current is a category of weak interactions in particle physics in which the exchanging gauge boson is the Z boson and no charged W± boson is produced in the process. In neutral-current processes, the interacting fermions scatter without changing their electric charge and without the creation of charged leptons or hadrons via W exchange. The Z boson couples to fermions through both vector and axial-vector components, leading to characteristic parity-violating effects.

In the electroweak theory developed by Glashow, Weinberg, and Salam, weak interactions occur in two classes: charged current interactions mediated by W± bosons and neutral current interactions mediated by Z bosons. Neutral currents are flavor-diagonal at tree level, so they do not change the type of fermion (for example, a neutrino remains a neutrino after neutral-current scattering). They can involve neutrinos or charged fermions in the initial and final states, as seen in neutrino-nucleon or neutrino-electron scattering.

Neutral currents were experimentally confirmed in the early 1970s, notably by experiments using the Gargamelle bubble chamber at CERN, providing crucial evidence for the electroweak unification and the existence of the Z boson. Since then, neutral-current processes have been studied extensively in deep inelastic scattering, collider experiments, and precision electroweak measurements. They remain essential for testing the Standard Model, determining the weak mixing angle, and constraining new physics such as additional neutral gauge bosons or nonstandard couplings.