Searching for Two-Neutrino and Neutrinoless Double Beta Decay of ${}^{134}$Xe with the PandaX-4T Experiment

Abstract

${}^{134}$Xe is a candidate isotope for neutrinoless double beta decay~($0\hat{I}½{\hat{I}}^2{\hat{I}}^2$) search. In addition, the two-neutrino case ($2\hat{I}½{\hat{I}}^2{\hat{I}}^2$) allowed by the Standard Model of particle physics has not yet been observed. Utilizing the 10.4% of ${}^{134}$Xe in the natural xenon in the PandaX-4T detector and its first 94.9-day exposure, we have established the most stringent constraints on $2\hat{I}½{\hat{I}}^2{\hat{I}}^2$ and $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ of ${}^{134}$Xe half-lives, with limits of $2.8\times 10^{22}$ yr and $3.0\times 10^{23}$ yr at 90% confidence level, respectively. The $2\hat{I}½{\hat{I}}^2{\hat{I}}^2$ ($0\hat{I}½{\hat{I}}^2{\hat{I}}^2$) limit surpasses the previously reported best result by a factor of 32 (2.7), highlighting the potential of large monolithic natural xenon detectors.