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

Abstract We study the two-neutrino double electron capture on 124Xe 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 β − 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 124Te ground state, we find half-lives T 1 / 2 2 ν ECEC = ( 1.3 − 18 ) × 10 22 y for the ET and T 1 / 2 2 ν ECEC = ( 0.43 − 2.9 ) × 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 124Xe 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 124Te.