Search for Double-Beta Decay of ${}^{130}\mathrm{Te}$ to the $0^{+}$ States of ${}^{130}\mathrm{Xe}$ with CUORE

Abstract

The CUORE experiment is a large bolometric array searching for the lepton number violating neutrino-less double beta decay ($0\hat{I}½{\hat{I}}^2{\hat{I}}^2$) in the isotope ${}^{130}\mathrm{Te}$. In this work we present the latest results on two searches for the double beta decay (DBD) of ${}^{130}\mathrm{Te}$ to the first $0_2^{+}$ excited state of ${}^{130}\mathrm{Xe}$: the $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ decay and the Standard Model-allowed two-neutrinos double beta decay ($2\hat{I}½{\hat{I}}^2{\hat{I}}^2$). Both searches are based on a 372.5 kg$\times$yr TeO${}_2$ exposure. The de-excitation gamma rays emitted by the excited Xe nucleus in the final state yield a unique signature, which can be searched for with low background by studying coincident events in two or more bolometers. The closely packed arrangement of the CUORE crystals constitutes a significant advantage in this regard. The median limit setting sensitivities at 90\% Credible Interval (C.I.) of the given searches were estimated as ${\mathrm{S}}_{1/2}^{0\hat{\mathrm{I}}½}=5.6\times 10^{24}\mathrm{yr}$ for the $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ decay and ${\mathrm{S}}_{1/2}^{2\hat{\mathrm{I}}½}=2.1\times 10^{24}\mathrm{yr}$ for the $2\hat{I}½{\hat{I}}^2{\hat{I}}^2$ decay. No significant evidence for either of the decay modes was observed and a Bayesian lower bound at $90\%$ C.I. on the decay half lives is obtained as: $({\mathrm{T}}_{1/2}{)}_{0_2^{+}}^{0\hat{\mathrm{I}}½}>5.9\times 10^{24}\mathrm{yr}$ for the $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ mode and $({\mathrm{T}}_{1/2}{)}_{0_2^{+}}^{2\hat{\mathrm{I}}½}>1.3\times 10^{24}\mathrm{yr}$ for the $2\hat{I}½{\hat{I}}^2{\hat{I}}^2$ mode. These represent the most stringent limits on the DBD of ${}^{130}$Te to excited states and improve by a factor $\sim 5$ the previous results on this process.

13 pages, 6 figures