Neutrino-less Double-Beta Decay with CUORE and the MAJORANA DEMONSTRATOR

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This grant partially supports neutrino research at the University of South Carolina (USC). The group studies the properties of the neutrino, the most prolific particle in the universe, about which much is still unknown. The primary effort is the search for the hypothesized, but not yet discovered, nuclear-radioactive decay called zero-neutrino double-beta decay. The existence of such a radioactive decay mode has important consequences. Its existence requires that neutrinos have mass, and that they are their own anti-particles. Most importantly, this process would require the violation of an important fundamental conservation law of elementary particle physics. The USC group has leadership roles in two of the leading experiments in this field: the MAJORANA DEMONSTRATOR, in the Sanford Underground Research Facility in South Dakota, and the Cryogenic Underground Observatory (CUORE) in the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. The spin-off technology from the required radiopurity of materials for the ultra-low background detectors has transitioned directly into Homeland Security. Four past USC PhD students from the program hold important positions in Homeland Security, at the Pacific Northwest and Savannah River National Laboratories. CUORE, nearing completion in the LNGS, is an array of 988 tellurium oxide single-crystal bolometers that operate at ~8-10 mK to search for the zero-neutrino decay of tellurium-130 (Te-130); the detector will contain 200-kg of Te-130. The predicted half-life sensitivity is ~10^(26) years, to reach into the inverted hierarchy neutrino-mass region. USC leads part of the R&D to determine the feasibility and cost of enriching CUORE to 93% in Te-130 from 33.4%, and equipping the bolometers with Cherenkov-light detectors to discriminate against alpha-particle background. These upgrades are designed to reach the sensitivity required to cover the inverted neutrino mass hierarchy. USC leads the CUORE data analysis to search for zero-neutrino double-beta decay of Te-130 to the first excited 0+ state in xenon-130, by detecting the coincidence events from the two electrons and cascade gamma rays. This technique achieved zero-background in the prototype experiment, CUORICINO. Finally, the USC group was responsible for the production of the CUORE front-end electronics, and will participate in its installation, commissioning and maintenance.