Next Generation Neutrinoless Double Beta Decay Experiments CUORE/CUORICINO (130Te) and Majorana (76Ge)

University South Carolina Research Foundation, Columbia SC

Investigators

Abstract

The neutrino is the lightest known elementary particle. It has no electric charge but has an intrinsic angular-momentum(or spin) of one half unit of Planck's constant just like it's cousin the electron. Discovered in 1957 by Reines and Cowan, it remains one of the least understood particles in the elementary zoo. According to conventional wisdom, in modern cosmology the universe is densely populated with neutrinos. Accordingly,if they would have a large enough mass, they could have played an important role in the evolution of the universe in it's early stages and even at present. Approximately 90% of the mass of the universe has not been identified. In 1998 it was announced that neutrinos resulting from the decay of cosmic-ray muons in the atmosphere were found to oscillate between different families. This would require that they do have some mass but such experiments do not yield how much. The rate of the hypothesized rare radioactive decay called double-beta decay can yield this very valuable information when combined with the neutrino oscillation results. The interesting version of this phenomenon would result if a nucleus would decay by emitting two electrons and nothing else. An important conservation law would be violated by such a process unless two anti-neutrinos were also emitted with the electrons. Since the electrons are leptons and the anti-neutrinos are anti-leptons the total number of leptons is conserved in the the decay with anti-neutrinos. For the decay to occur without anti-neutrinos, neutrinos in general must have mass and an important symmetry in physics must be violated. The Majorana and CUORE experiments, which are the subjects of this proposal, are next generation no-neutrino double-beta decay experiments with an improvement in the sensitivity to neutrino mass that is predicted to be about one hundred times better than the best experiments done to date. Considering all the data available, they have a significant probability for discovery, for being able to provide important information on the mass of neutrinos as well as to determine if neutrinos are there own anti-particles. CUORICINO is a smaller first step towards building the full version of CUORE.