Neutrinoless Double-Beta Decay Search by CUORE Experiment
Abstract: CUORE (Cryogenic Underground Observatory for Rare Events) is the first ton-scale experiment whose main goal is the search for neutrinoless double-beta decay in 130Te with a segmented array of TeO2 bolometers operated at cryogenic temperatures. After construction and commissioning, the CUORE detector is finally operational and has been taking science data since the first months of 2017. CUORE-0, the first tower of CUORE, an array of 52 TeO2 crystals, operated between 2013 and 2015 as a full CUORE prototype. The large amount of data collected by CUORE-0 makes it ideal for studying the performance of bolometric detectors in detail.
The bolometric technique is based on measuring the energy released by an interacting particle converted into phonons. The goal of my analysis is the study of the CUORE-0 bolometer response and behavior for a better understanding of the detector and possible improvement of experimental sensitivity. Finding the different components of the CUORE-0 pulses and correlating them to physics parameters will allow a better understanding of the detectors and possible improvement of performance. In my analysis, I first defined a set of variables to describe the pulse shape. Then I studied the correlation between pulse shape parameters and physical parameters. This study provided, for the first time, a function model that describes the CUORE pulse shape that is capable of identifying the dominant thermal capacitance of the CUORE thermal model. A relevant outcome of my analysis is that the heat capacity produced by the presence of platinum fragments inside the crystals must be taken into account in the CUORE thermal model.
The CUORE bolometer are housed in a dedicated custom-built cryogenic-free dilution refrigerator, which must guarantee extremely radio-purity of each component, to reach a base temperature in stable condition, by mechanical decoupling between detector and cryogenic system to minimize the noise induced by cryostat vibration. Before the detector installation, several cold runs were done in order to reach the base temperature and validate the cryogenic system performances. In the last cold run, with full load except the detector, the system reached a base temperature of (6:3 ± 0:04) mK in stable conditions.