Open Access Publications from the University of California

## Searching for 0νββ Decay with CUORE and CUPID

Abstract

Since they were first postulated, neutrinos have been one of the most mysterious fundamental particles known to us. The discovery of neutrino oscillation has shown that contrary to our original assumptions, neutrinos are not all massless. This has renewed interest in the idea of Majorana neutrinos as an explanation for the small but nonzero neutrino masses, and the search for neutrinoless double-beta ($0\nu\beta\beta$) decay is currently the most sensitive way to probe this possibility. An observation of this process would constitute the first example of violation of lepton number conservation, demonstrate that neutrinos have a Majorana nature, and help set the scale of their absolute masses. CUORE (Cryogenic Underground Observatory for Rare Events) is one of the leading experiments in the current international program looking for evidence of $0\nu\beta\beta$ decay.

In part I of this dissertation I present a $0\nu\beta\beta$ search based on analysis of CUORE data from its first tonne-year of $^{\textrm{nat}}$TeO$_2$ exposure, corresponding to 288.8 kg$\cdot$yr of $^{130}$Te exposure. We observe no evidence of $0\nu\beta\beta$ decay of $^{130}$Te and set a Bayesian 90\% C.I. lower limit on the corresponding half-life of $T^{0\nu}_{1/2} > 2.2\times10^{25}$ years, as well as a Frequentist 90\% C.L. lower limit of $T^{0\nu}_{1/2} > 2.6\times10^{25}$ years.

As CUORE continues to take data, efforts are already underway to build towards its eventual successor CUPID (CUORE Upgrade with Particle ID). In part II of this dissertation I present the work I have contributed towards the realization of CUPID, including light yield characterization and simulation for TeO$_2$, analysis efforts for the CUPID-Mo demonstrator, and the development of cryogenic front-end electronics for CUPID.