Sensitivity of the NEXT experiment to Xe-124 double electron capture

Abstract

Double electron capture by proton-rich nuclei is a second-order nuclear process analogous to double beta decay. Despite their similarities, the decay signature is quite different, potentially providing a new channel to measure the hypothesized neutrinoless mode of these decays. The Standard-Model-allowed two-neutrino double electron capture ($2\nu ECEC$) has been predicted for a number of isotopes, but only observed in ${}^{78}$Kr, ${}^{130}$Ba and, recently, ${}^{124}$Xe. The sensitivity to this decay establishes a benchmark for the ultimate experimental goal, namely the potential to discover also the lepton-number-violating neutrinoless version of this process, $0\nu ECEC$. Here we report on the current sensitivity of the NEXT-White detector to ${}^{124}$Xe $2\nu ECEC$ and on the extrapolation to NEXT-100. Using simulated data for the $2\nu ECEC$ signal and real data from NEXT-White operated with ${}^{124}$Xe-depleted gas as background, we define an optimal event selection that maximizes the NEXT-White sensitivity. We estimate that, for NEXT-100 operated with xenon gas isotopically enriched with 1 kg of ${}^{124}$Xe and for a 5-year run, a sensitivity to the $2\nu ECEC$ half-life of $6\times 10^{22}$ y (at 90% confidence level) or better can be reached.

arXiv comment23 pages, 13 figures

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Cited by in corpus (2)

• Theoretical analysis and predictions for the double electron capture of ${}^{124}$Xe
• Large-scale shell-model study of 2$\nu$ECEC process in ${}^{78}$Kr