Background determination for the LUX-ZEPLIN dark matter experiment

Abstract

The LUX-ZEPLIN experiment recently reported limits on WIMP-nucleus interactions from its initial science run, down to 9.2 × 10−48 cm2 for the spin-independent interaction of a 36 GeV=c2 WIMP at 90% confidence level. In this paper, we present a comprehensive analysis of the backgrounds important for this result and for other upcoming physics analyses, including neutrinoless double-beta decay searches and effective field theory interpretations of LUX-ZEPLIN data. We confirm that the in-situ determinations of bulk and fixed radioactive backgrounds are consistent with expectations from the ex-situ assays. The observed background rate after WIMP search criteria were applied was ð6.3 0.5Þ × 10−5 events=keVee=kg=day in the low-energy region, approximately 60 times lower than the equivalent rate reported by the LUX experiment.