Low-level radioactive decay in which particles, usually an electron with an antineutrino, or less commonly a positron with an antineutrino, are emitted.
Precision measurements of neutron beta decay correlations, a, b, B, and A, provide important tests of the electroweak standard model: a test of unitarity of the first row of the CKM matrix, a test of the CVC hypothesis, and a sensitive search for right-handed currents or scalar or tensor bosons.
Drexlinb et al., "KATRIN-a next generation tritium beta decay experiment with sub-eV sensitivity for the electron neutrino mass," http://xxx.lanl.gov/abs/hepex/0109033.
Around 1930, an anomaly in the important nuclear transformation process called beta decay gave physicist Wolfgang Pauli the occasion to postulate the neutrino's existence.