REVIEW OF DOUBLE BETA DECAY EXPERIMENTS

Abstract

The type of double beta decay (two-neutrino) which must occur via a second order weak interaction has finally been observed in the laboratory, and the result agrees with previous geochemical determinations. Calculations can be made to agree with these experiments by adding a particle-particle force to decrease the rate, but the additional force may not have a large effect on predictions of no-neutrino double beta decay. The latter, which requires lepton-number violation and one other element of new physics beyond the standard model (such as neutrino mass) could occur in at least two forms. One of these, Majoron-induced decay, has definitely not been observed so far, contrary to an earlier experimental result. The other form of neutrinoless decay is also not yet observed, the lifetime limit being about 1024 years. This limit can be used to set constraints on effective Majorana neutrino mass (~2eV), heavy Majorana neutrino mass, right-handed currents, and supersymmetric particles in theories with R parity violation.