Q value and half-life of double-electron capture in Os-184

TL;DR

This study assesses Os-184 as a candidate for neutrinoless double-electron capture, combining precise mass measurements and nuclear calculations, concluding its transition half-life exceeds 10^{29} years, making it less promising.

Contribution

It provides high-precision mass measurements and nuclear matrix element evaluations for Os-184, clarifying its suitability for neutrinoless double-electron capture searches.

Findings

Resonant enhancement energy excess is -8.89(58) keV.

Half-life exceeds 1.3 x 10^{29} years for 1 eV neutrino mass.

Strong suppression of transition due to nuclear deformation.

Abstract

Os-184 has been excluded as a promising candidate for the search of neutrinoless double-electron capture. High-precision mass measurements with the Penning-trap mass spectrometer TRIGA-TRAP resulted in a marginal resonant enhancement with = -8.89(58) keV excess energy to the 1322.152(22) keV 0+ excited state in W-184. State-of-the-art energy density functional calculations are applied for the evaluation of the nuclear matrix elements to the excited states predicting a strong suppression due to the large deformation of mother and daughter states. The half-life of the transition in Os-184 exceeds T_{1/2} > 1.3 10^{29} years for an effective neutrino mass of 1 eV.