CUORE: A Cryogenic Underground Observatory for Rare Events

Abstract

Recently, neutrino oscillation experiments have unequivocally demonstrated that neutrinos have mass and mix. These experiments have yielded valuable information on the mixing angles and on the mass differences of the three eigenstates but cannot determine the scale of the neutrino mass, which is fixed by the lightest neutrino mass eigenvalue. This can only be directly determined by kinematic measurementsor by the observation and measurement of the neutrinoless double-beta decay (NDBD) half-life. The CUORE experiment is designed with a sensitivity capable of probing the range indicated by oscillation experiments. It consists of an array of 988, 750 g, TeO2 bolometers operating at 8 to 10 mK and arranged in a cylindrical geometry of 19 towers hanging on the bottom of the mixing chamber of a dilution refrigerator. Each tower consists of 13 4-detector modules for a total of 52 bolometers. One such tower has been successfully constructed and is now operated in the Gran Sasso Laboratory as a test experiment, and also as an independent NDBD experiment called CUORICINO. In fact, the 3 year half-life sensitivity of CUORICINO for NDBD decay of 130Te is 6.1E24 years. Thus far the CUORICINO data demonstrate the technical feasibility of the expanded CUORE array while showing what and where the sources of background are and how to reduce them. A background reduction to 0.01 counts/keV/kg/y in the NDBD energy region is therefore possible. This would allow the full CUORE array to achieve a 5-year sensitivity of the order of 30 meV on the effective neutrino mass. Another order of magnitude reduction (corresponding to a sensitivity of about 15 meV) will present a real challenge, but is also possible. The CUORE experiment will be installed in the Laboratori Nazionali del Gran Sasso (LNGS) in Assergi, Italy.