Search for neutrinoless double-electron capture ofDy156

Abstract

Background: Multiple large collaborations are currently searching for neutrinoless double-$\ensuremath{\beta}$ decay, with the ultimate goal of differentiating the Majorana-Dirac nature of the neutrino.Purpose: Investigate the feasibility of resonant neutrinoless double-electron capture, an experimental alternative to neutrinoless double-$\ensuremath{\beta}$ decay.Method: Two clover germanium detectors were operated underground in coincidence to search for the de-excitation $\ensuremath{\gamma}$ rays of $^{156}\mathrm{Gd}$ following the neutrinoless double-electron capture of $^{156}\mathrm{Dy}$. 231.95 d of data were collected at the Kimballton underground research facility with a 231.57 mg enriched $^{156}\mathrm{Dy}$ sample.Results: No counts were seen above background and half-life limits are set at $O({10}^{16}\text{--}{10}^{18})$ yr for the various decay modes of $^{156}\mathrm{Dy}$.Conclusion: Low background spectra were efficiently collected in the search for neutrinoless double-electron capture of $^{156}\mathrm{Dy}$, although the low natural abundance and associated lack of large quantities of enriched samples hinders the experimental reach.