Background Determination for the LUX-ZEPLIN (LZ) Dark Matter Experiment

TL;DR

This paper provides a detailed background analysis for the LUX-ZEPLIN dark matter experiment, confirming background levels and supporting future physics analyses including WIMP searches and neutrinoless double-beta decay.

Contribution

It offers a comprehensive background determination methodology and validates in-situ background estimates against ex-situ assays for LZ data.

Findings

Background rate after WIMP search criteria was (6.3±0.5)×10^{-5} events/keV_{ee}/kg/day.

Background levels are consistent with expectations from assays.

Background rate is approximately 60 times lower than previous LUX results.

Abstract

The LUX-ZEPLIN experiment recently reported limits on WIMP-nucleus interactions from its initial science run, down to $9.2\times10^{-48}$ cm$^2$ for the spin-independent interaction of a 36 GeV/c$^2$ 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 $(6.3\pm0.5)\times10^{-5}$ events/keV$_{ee}$/kg/day in the low-energy region, approximately 60 times lower than the equivalent rate reported by the LUX experiment.