Charge-to-light signatures of inner-shell vacancies in xenon time projection chambers

Dark matter searches using dual-phase xenon time projection chambers (LXe-TPC) rely on the discrimination between electronic recoils (background) and nuclear recoils (signal) based on the ratio of ionization electrons to scintillation photons produced by the interaction. This discrimination is calibrated at low energies using β-decays of tritium. Neutrino and Compton scatters from inner-shell electrons of Xe atoms can result in the emission of Auger electrons and x-rays in addition to the primary recoiling electron, and thus have a different event topology than β-decays. Due to their low energy and large numbers, these secondary particles can deposit large amounts of energy within a small radius, which is uncharacteristic of valence electron recoils and is more akin to nuclear recoils. This effects the profile of the ν-e scattering background in a way that is unaccounted for in LXe-TPC dark matter searches, and presents the possibility of a false discovery claim. The XELDA detector has been constructed to study the electron capture decay of ¹²⁷Xe to produce a high-purity sample of inner-shell vacancies accompanied by an Auger cascade. In this talk, I present an overview of the XELDA detector system, calibrations, and preliminary results of the ¹²⁷Xe analysis.