Search for Neutrinoless $\beta^+EC$ Decay of $^{120}$Te with CUORE

TL;DR

This study searches for neutrinoless positron emitting electron capture decay in $^{120}$Te using CUORE, setting new lower limits on the decay half-life and demonstrating the detector's capability for rare event searches beyond its primary goal.

Contribution

First search for $0 ueta^+EC$ decay in $^{120}$Te with CUORE, improving existing limits by an order of magnitude and utilizing multiple event topologies for enhanced sensitivity.

Findings

No evidence of $0 ueta^+EC$ decay was observed.

Set a new lower limit of $2.9 imes 10^{22}$ years on the half-life.

Achieved a median sensitivity of $3.4 imes 10^{22}$ years.

Abstract

CUORE is a large scale cryogenic experiment searching for neutrinoless double beta decay ($0\nu\beta\beta$) in $^{130}$Te. The CUORE detector is made of natural tellurium, providing the possibility of rare event searches on isotopes other than $^{130}$Te. In this work we describe a search for neutrinoless positron emitting electron capture ($0\nu\beta^+EC$) decay in $^{120}$Te with a total TeO$_2$ exposure of 355.7 kg $\cdot$ yr, corresponding to 0.2405 kg $\cdot$ yr of $^{120}$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 $0\nu\beta^+EC$ 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 $3.4 \cdot 10^{22}$ yr at 90% Credibility Interval (C.I.). After unblinding we find no evidence of $0\nu\beta^+EC$ signal and set a 90% C.I. Bayesian lower limit of $2.9 \cdot 10^{22}$ yr on $^{120}$Te half-life. This result improves by an order of magnitude the existing limit from the combined analysis of CUORE-0 and Cuoricino.