The search for neutrinoless double beta decay of 130Te and 120Te with the CUORE experiment
Creators: name: CAMPANI, ALICE
Publisher: name: Universit� degli studi di Genova
Year: 2021

description: The discovery of neutrino masses through the observation of oscillations has boosted the importance of neutrinoless double beta decay (0???). This rare process is a direct probe of Beyond the Standard Model Physics, since it violates the lepton number by two units. Furthermore, 0??? allows us to investigate the Dirac/Majorana nature of the neutrino and to get information on the neutrino absolute mass scale and ordering. This thesis work is developed in the framework of the CUORE experiment. CUORE (Cryogenic Underground Observatory for Rare Events) is a tonne-scale bolometric experiment whose main goal is the search for the 0??? of 130Te. The experiment is currently taking data at the Laboratori Nazionali del Gran Sasso (Italy). In the first part of the thesis, the Physics of interest for CUORE and the experimental aspects are introduced. A general overview of the current knowledge in neutrino physics is presented. 0??? process is introduced within the particle physics scenario in which the Majorana mass of ordinary neutrinos dominate the decay rate. Then, the experimental challenge the observation of double beta decay represents is discussed. After a general overview of the bolometric technique for rare events search, a general description of the CUORE experiment is outlined. Details on the main components of the CUORE detector are provided, focusing on the stringent requirements in terms of background and noise reduction they must satisfy. Finally, we illustrate the calibration system of the CUORE detector, comparing two alternative approaches employed in terms of compliance with the cryogenic infrastructure and performance. The second part of the thesis focuses on the data processing chain. The most important stages of the low level data analysis include the evaluation of signal amplitude, the energy calibration and the identification of coincident events between the detectors. We present a preliminary analysis of the improvements we obtain in the background reconstruction with the optimum trigger and discuss the performance of the external detector calibration system. Finally, we describe the steps to characterise our detector in terms of efficiency of the selection cuts and energy response function. The core of the thesis focuses on two physical analysis, the search for 0??? decay of 130Te with a total TeO2 exposure of 372.5 kg � yr, and the search for neutrinoless double emitting electron capture (0?EC?+) decay of 120Te with 355.7 kg � yr TeO2 exposure. The data selection and the fit strategy for the search of 0??? decay in 130Te are discussed in detail. An interpretation of the final result on the 0??? decay rate estimate is given, with an overview of the major sources of uncertainty on the final results. Then, we present the analysis of a specific double beta decay mode of 120Te. We start introducing the motivations behind a growing interest for the (neutrinoless) double beta decay modes different from ????, where electrons are emitted. Then, we describe the physical process analyzed in this dissertation, pointing out the requirements we set to identify candidate signal events. We discuss our data selection, specifying differences with respect to the 0??? decay analysis of 130Te and we illustrate the statistical approach. Given the complexity of this analysis a preliminary result on the 120Te rate for 0?EC?+ is presented, and the future developments of this study are also introduced.