Dissertation Defense: Christopher Davis, Yale University, “Search for Neutrinoless Double Beta Decay with Majoron Emission in CUORE”

This thesis describes a search performed at the Cryogenic Underground Observatory for Rare Events (CUORE) for Majoron-emitting neutrinoless double-beta decays. A discovery of any form of neutrinoless double-beta decay would be of immense importance to the field of physics, as any mechanism by this decays occurs would require physics beyond the Standard Model. In addition, neutrinoless double-beta decays, including type I Majoron models, would show that lepton number is not a conserved quantity and, along with other measurements, could explain the prevalence of matter over antimatter in the early universe. Also described in this thesis is the experiment, CUORE, which is a neutrinoless double-beta decay experiment currently in operation at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, along with a detailed description of one of the calibration systems used in the experiment. Since April 2017, CUORE has been taking physics data using 988 TeO2 crystals arranged in 19 towers inside of a custom cryostat operating at approximately 10 mK. The results presented in this thesis correspond to a live-time of 216.36 kg yr in TeO2 and place lower limits (90% C.L.) for majoron decays of spectral index 1, 2, 3, and 7, respectively. These results are the strongest limits in Te-130 to date, and limits produced for coupling constants of each majoron decay mode are comparable to that of other present experiments. Lastly, these searches for majoron decays continue to be an interesting phase space for research into neutrinoless double-beta decay, and serve as another promising decay mode to observe as detector technology and background reduction techniques improve.
Thesis Advisor: Reina Maruyama (reina.maruyama@yale.edu)