Abstract

Two-neutrino double electron capture is a rare nuclear decay where two electrons are simultaneously captured from the atomic shell. For 124^{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^{124}Xe using 7636 kg\cdotd 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 T1/2>6.5×1020T_{1/2}>6.5\times10^{20} yr. We also evaluated the sensitivity of the XENON1T experiment, which is currently being commissioned, and find a sensitivity of T1/2>6.1×1022T_{1/2}>6.1\times10^{22} yr after an exposure of 2 t\cdotyr

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