Measurement of charge and light yields for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Xe</mml:mi></mml:mrow><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>127</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>L</mml:mi></mml:math> -shell electron captures in liquid xenon

Dark matter searches using dual-phase xenon time-projection chambers (LXe-TPCs) rely on their ability to reject background electron recoils (ERs) while searching for signal-like nuclear (NRs). ER response is typically calibrated $\beta$-decay sources, such as tritium, but these calibrations do not characterize events accompanied by an atomic vacancy, in solar neutrino scatters off inner shell electrons. Such lead emission of X-rays and Auger electrons, resulting higher electron-ion recombination thus a more NR-like than inferred from calibration. We present cross-calibration tritium $\beta$-decays $^{127}$Xe electron-capture decays (which produce inner-shell vacancies) small-scale LXe-TPC give the most precise measurements date light charge yields L-shell liquid xenon. observe 6.9$\sigma$ (9.2$\sigma$) discrepancy capture relative $\beta$-decays, measured at drift field 363 $\pm$ 14 V/cm (258 13 V/cm), when compared simulations tuned reproduce correct response. In dark searches, use model that neglects this effect leads overcoverage (higher limits) background-only multi-kiloton-year exposures, level much less 1-$\sigma$ experiment-to-experiment variation 90\% C.L. upper limit interaction rate 50 GeV/$c^2$ particle.