Search for Neutrinoless Double Beta Decay with the NEMO-3 and SuperNEMO Experiments

University Of Texas At Austin, Austin TX

Investigators

Abstract

Neutrinos are some of the most intriguing elementary particles that make up the Standard Model of particle physics. They were long thought to have no mass, don?t interact with much of anything, and may hold the key to why there is more matter than antimatter in the Universe. Neutrinos are commonly observed in beta decay, a radioactive process that involves the emission of an electron (or its antiparticle the positron) from the nucleus, and which is always accompanied by the emission of a neutrino (or its antiparticle the antineutrino) as well. This research focuses on the search for what is called neutrino-less double beta decay, where an initial nucleus with atomic weight and number (A,Z) is transformed into a nucleus of (A, Z + 2) with the emission of only two electrons and nothing else. According to the Standard Model of particle physics, this can only happen if neutrinos and antineutrinos are exactly the same, that is, the neutrino is its own antiparticle. It is believed that this overlap between matter and antimatter could prove essential in answering one of the most fundamental questions in science: why is our Universe made exclusively of matter? The research uses the NEMO-3 and SuperNEMO experiments. The NEMO-3 experiment employed thin foils of particular nuclear isotopes surrounded by detectors that could provide 3D particle tracking of the decay electrons. This unique technique provides several observables for each registered event, offering a powerful means to identify double beta decays and to reject background processes. SuperNEMO will further exploit the NEMO-3 technique. The research group supported by this award will continue its participation in the NEMO-3 data analysis and in the construction of the first SuperNEMO module ("Demonstrator"). Through their activities, the group will educate and train young researchers in building state-of-the-art research instruments and science projects. They will work towards building on the University of Texas at Austin campus an exhibit gallery illustrating the discovery, the underlying physics, and applications of natural radioactivity, cosmic rays, and related subatomic phenomena. The NEMO-3 analysis has already yielded high precision measurements of double beta half-lives for seven isotopes and set some of the most stringent constraints on the neutrino-less transitions, yielding an upper limit for the effective neutrino mass of (0.3-0.9)eV, where the span reflects uncertainties in the nuclear matrix element. The SuperNEMO aspects include designing and fabrication of the central source foil frame, the light injection and calorimeter monitoring system, and the Bi-207 calibration deployment. For the next three years, a critical period for completing and commissioning the Demonstrator, the group will complete hardware commitments and will participate in analysis of data from the new experiment.