Measurement of charge and light yields for Xe 127 L -shell electron captures in liquid xenon

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Measurement of charge and light yields for Xe 127 L -shell electron captures in liquid xenon

Temples, DJ; McLaughlin, J; Bargemann, J; Baxter, D; Cottle, A; Dahl, CE; Lippincott, WH; ... Phelan, J; + view all (2021) Measurement of charge and light yields for Xe 127 L -shell electron captures in liquid xenon. Physical Review D , 104 (11) , Article 112001. 10.1103/PhysRevD.104.112001. Green open access

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Abstract

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 recoils (NRs). ER response is typically calibrated using β-decay sources, such as tritium, but these calibrations do not characterize events accompanied by an atomic vacancy, as in solar neutrino scatters off inner-shell electrons. Such events lead to emission of x rays and Auger electrons, resulting in higher electron-ion recombination and thus a more NR-like response than inferred from β-decay calibration. We present a cross-calibration of tritium β-decays and Xe127 electron-capture decays (which produce inner-shell vacancies) in a small-scale LXe-TPC and give the most precise measurements to date of light and charge yields for the Xe127 L-shell electron-capture in liquid xenon. We observe a 6.9σ (9.2σ) discrepancy in the L-shell capture response relative to tritium β decays, measured at a drift field of 363±14 V/cm (258±13 V/cm), when compared to simulations tuned to reproduce the correct β-decay response. In dark matter searches, use of a background model that neglects this effect leads to overcoverage (higher limits) for background-only multi-kiloton-year exposures, but at a level much less than the 1-σ experiment-to-experiment variation of the 90% C.L. upper limit on the interaction rate of a 50 GeV/c2 dark matter particle.

Type:	Article
Title:	Measurement of charge and light yields for Xe 127 L -shell electron captures in liquid xenon
Open access status:	An open access version is available from UCL Discovery
DOI:	10.1103/PhysRevD.104.112001
Publisher version:	https://doi.org/10.1103/PhysRevD.104.112001
Language:	English
Additional information:	This version is the version of record. For information on re-use, please refer to the publisher's terms and conditions.
UCL classification:	UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI:	https://discovery.ucl.ac.uk/id/eprint/10177767