Limit on Lepton Nonconservation and Neutrino Mass from Double Beta Decay

Abstract

A lower limit of 5×${10}^{22}$ yr (68% confidence level) has been obtained for the half-life of the neutrinoless double beta decay of ${}_{}{}^{76}{}_{}{}^{}\mathrm{Ge}$. This process would require lepton-number nonconservation and that the electron neutrino have a mass and/or the weak interaction have right-handed currents. Ge detectors of 178 and 158 ${\mathrm{cm}}^3$ were used inside a NaI active shield for 1618 h. The radioactivity background was kept so low that, despite operating above ground, there was only 2×${10}^{-3\mathrm{}}$ count/keV·h total at the expected 2.041-MeV peak.