Precise Determination of the GERMANIUM-76-SELENIUM -76 Atomic Mass Difference and the Majorana Mass of the Electron Neutrino

The double-beta decay process observed in ^{82}Se has been, until now, the rarest decay process ever observed in the laboratory. The lifetime has been measured to be of the order of 10 ^{21} years. The postulated form of the double-beta decay known as the zero-neutrino mode, or betabeta(0 nu), violates several of the principles of the Standard Model of physics. This decay form, applied to the candidate nucleus ^{76} Ge, would require the decay of two neutrons to two protons and the emission of only two electrons, violating conservation of lepton number and requiring the neutrino to be a Majorana particle. In addition, the neutrino would have to be massive and/or participate in a righthanded weak current process. Since this decay would emit only electrons, its signature would be a characteristic sharp spike at the Q-value for the decay. There are currently a number of research groups searching for evidence of the betabeta(0nu) decay of ^{76}Ge. Measurement by Ellis et al. in 1985 established the Q-value for the ^{76}Ge -^{76}Se decay. New measurements have cast some doubt on this determination, and, in the interests of resolving the controversy, a re-measurement has been made. The new results of mass measurements on mass doublets in this area will be given. In addition, the implication of this new Q-value to the mass of the neutrino will be discussed. New limits on the neutrino mass will be derived.