Two-neutrino double electron capture on $^{124}$Xe based on an effective theory and the nuclear shell model

TL;DR

This study estimates the half-life of two-neutrino double electron capture on $^{124}$Xe using effective theory and shell model approaches, indicating potential observability in upcoming experiments.

Contribution

It provides the first comprehensive half-life predictions for $^{124}$Xe double electron capture using two advanced nuclear models, with uncertainties and experimental implications.

Findings

Half-life estimates range from 0.43 to 18 x 10^{22} years.

Predictions are consistent with current experimental limits.

Results suggest the process could be observed in near-future experiments.

Abstract

We study the two-neutrino double electron capture on $^{124}$Xe based on an effective theory (ET) and large-scale shell model calculations, two modern nuclear structure approaches that have been tested against Gamow-Teller and double-beta decay data. In the ET, the low-energy constants are fit to electron capture and $\beta^{-}$ transitions around xenon. For the nuclear shell model, we use an interaction in a large configuration space that reproduces the spectroscopy of nuclei in this mass region. For the dominant transition to the $^{124}$Te ground state, we find half-lives $T^{2\nu{\rm ECEC}}_{1/2}=(1.3-18)\times 10^{22}$ y for the ET and $T^{2\nu{\rm ECEC}}_{1/2} = (0.43-2.9)\times 10^{22}$ y for the shell model. The ET uncertainty leads to a half-life almost entirely consistent with present experimental limits and largely within the reach of ongoing experiments. The shell model half-life range overlaps with the ET, but extends less beyond current limits. Our findings thus suggest that the two-neutrino double electron capture on $^{124}$Xe has a good chance to be discovered by ongoing or future experiments. In addition, we present results for the two-neutrino double electron capture to excited states of $^{124}$Te.