Antineutrino

An antineutrino is the antiparticle of the neutrino, a fermion with spin 1/2 and no electric charge. In the Standard Model, there are three flavors of antineutrinos corresponding to the three neutrino flavors: electron, muon, and tau. In the Dirac framework, neutrinos and antineutrinos are distinct particles that carry opposite lepton numbers; in a Majorana framework, a neutrino could be its own antiparticle and the distinction between neutrino and antineutrino can blur.

Antineutrinos interact with matter only through the weak nuclear force (and gravity), giving them an extremely small interaction probability. They can be produced in beta-minus decay (for example, neutron decay to proton, electron, and an electron antineutrino) and in various processes in nuclear reactors and astrophysical sources. They are commonly detected via inverse beta decay, where an electron antineutrino converts a proton into a neutron and a positron; this reaction has a threshold of 1.806 MeV and is often observed with delayed neutron capture in large detectors.

In practice, experiments study electron antineutrinos from reactors or geoneutrinos and, less commonly, from astrophysical events. Measurements of antineutrinos have been crucial for understanding neutrino oscillations, the phenomenon that causes flavor change as neutrinos propagate.