Search for Two-Neutrino Double Electron Capture of $^{124}$Xe with XENON100

Understand

Two-neutrino double electron capture is a rare nuclear decay where two electrons are simultaneously captured from the atomic shell.

• For $^{124}$Xe this process has not yet been observed and its detection would provide a new reference for nuclear matrix element calculations.
• We have conducted a search for two-neutrino double electron capture from the K-shell of $^{124}$Xe using 7636 kg$\cdot$d of data from the XENON100 dark matter detector.
• Using a Bayesian analysis we observed no significant excess above background, leading to a lower 90 % credibility limit on the half-life $T_{1/2}>6.5\times10^{20}$ yr.