Search for Two-Neutrino Double-Beta Decay of ¹³⁰Te to Excited States of ¹³⁰Xe with CUORE​

The CUORE experiment is a ton-scale search for neutrinoless double-beta decay (0υββ) composed of an array of 988 tellurium dioxide crystals, each instrumented as a cryogenic macrocalorimeter. While a discovery of 0υββ would herald new physics, the Standard Model process of two-neutrino double-beta decay (2υββ) in ¹³⁰Te is readily measured by CUORE. However, still unobserved in ¹³⁰Te are decays wherein the daughter ¹³⁰Xe nucleus is left in an excited state which subsequently decays via gamma emission, leading to events with energy deposited across multiple crystals. Understanding the branching ratio and spectral shape for such 2υββ decays to excited states can improve nuclear modelling and help constrain the matrix elements involved in searches for neutrinoless double-beta decay. In this talk, I describe progress towards an improved search for 2υββ decays to excited states with an increased exposure of CUORE. This analysis showcases feature selection and event classification tools which exploit CUORE's segmented geometry to increase signal sensitivity.​