Investigation of background sources and search for neutrinoless double-beta decay in CUORE

The Cryogenic Underground Observatory for Rare Events (CUORE) experiment at Gran Sasso National Laboratory in Italy searches for neutrinoless double-beta (0νββ) decay of Te-130. The experimental sensitivity relies heavily on the background rate in the 0νββ decay region of interest (ROI). In CUORE, the dominant source of background in the ROI are degraded alpha particles originating from contaminated surfaces facing the detector.This dissertation focuses on the work toward developing a detailed background model of the CUORE physics data in the ∼3 MeV – 7 MeV energy region, in order to identify and constrain the alpha background contribution to the ROI. A subset of the CUORE physics data collected between March 2019 and November 2020, corresponding to 433.3 kg�yr exposure TeO2, was used to identify the background sources contributing to the alpha energy region. Multiplicity information, based on the number of CUORE crystals that detect energy depositions within a given space-time window, was used to distinguish bulk and surface contaminations. Monte Carlo simulations of the energy spectra of the identified background sources were used to constrain the characteristic depths of the surface contaminations used in the background model. This detailed study of the background alpha spectrum shape complements to previous background source investigations that used very coarse spectrum binning and allowed us to examine features of the detector energy response that depend on the depth of the surface contaminations