Optimization of the CUORE detector during the commissioning phase

This thesis work is developed in the framework of the CUORE experiment. CUORE (Cryogenic Underground Observatory for Rare Events) is presently (January 2017) in the initial phase of the detector commissioning at the Laboratori Nazionali del Gran Sasso (Italy). CUORE will search for the neutrinoless double beta decay (0νββ) of 130Te with an array of 988 bolometers. The first part of the thesis introduces the Physics and the technology of interest for CUORE. In particular, the general overview of 0νββ is inserted within the frame of the current theoretical understanding, and the results of original works and analyses are reported. Concerning the introduction to bolometers, a wider and technical overview is followed by the more specific description of the use of TeO2 crystals for the 0νββ search, briefly summarizing the long chain of experiments leading to CUORE and stressing the importance of the recent results coming from the CUORE-0 detector. The core of the thesis focuses on the commissioning of the CUORE experimental apparatus. After a detailed description of the cryogenic system, the relevant steps of the commissioning phase are reviewed. In particular, the analyses of the cryogenic data are presented together with the developments that allowed the cryostat to reach its final configuration, and thus be ready to host the CUORE detector. The final part is devoted to the description of the analysis and of the results obtained with the first prototype detector operated as a bolometer inside the CUORE cryostat. In fact, its study proved to be fundamental to understand how to optimize the system cryogenic performance in view of the forthcoming (much complex) CUORE detector. The CUORE cryostat commissioning phase was long and complex, but indeed an indispensable prerequisite for a stable and long operation in extreme conditions of low temperature, noise and activity, opening the way to one of the most sensitive search for 0νββ.