The Cryogenic Underground Observatory for Rare Events (CUORE) is a large-scale cryogenic experiment searching for neutrinoless double-beta decay ($0\nu \beta \beta$) in ${}^{130}\mathrm{Te}$. The CUORE detector is made of natural tellurium, providing the possibility of rare event searches on isotopes other than ${}^{130}\mathrm{Te}$. In this work we describe a search for neutrinoless positron-emitting electron capture (${\beta }^{+}\mathrm{EC}$) decay in ${}^{120}\mathrm{Te}$ with a total ${\mathrm{TeO}}_2$ exposure of 355.7 kg yr, corresponding to 0.2405 kg yr of ${}^{120}\mathrm{Te}$. Albeit $0\nu \beta \beta$ with two final-state electrons represents the most promising channel, the emission of a positron and two 511-keV $\gamma$'s make $0\nu {\beta }^{+}\mathrm{EC}$ decay signature extremely clear. To fully exploit the potential offered by the detector modularity we include events with different topology and perform a simultaneous fit of five selected signal signatures. Using blinded data we extract a median exclusion sensitivity of $3.4\times {10}^{22}$ yr at 90% credibility interval (C.I.). After unblinding we find no evidence of $0\nu {\beta }^{+}\mathrm{EC}$ signal and set a 90% C.I. Bayesian lower limit of $2.9\times {10}^{22}$ yr on ${}^{120}\mathrm{Te}$ half-life. This result improves by an order of magnitude the existing limit from the combined analysis of CUORE-0 and Cuoricino.

• Received 25 March 2022
• Accepted 27 May 2022

DOI:https://doi.org/10.1103/PhysRevC.105.065504