Limit on Lepton Nonconservation and Neutrino Mass from Double Beta Decay

Abstract

A lower limit of 5\ifmmode\times\else\texttimes\fi{}${10}^{22}$ 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\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ count/keV\ifmmode\cdot\else\textperiodcentered\fi{}h total at the expected 2.041-MeV peak.