The LUX-ZEPLIN experiment recently reported limits on WIMP-nucleus interactions from its initial science run, down to $9.2\times {10}^{-48}{\mathrm{cm}}^2$ for the spin-independent interaction of a $36\mathrm{GeV}/{\mathrm{c}}^2$ 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 $(6.3\pm 0.5)\times {10}^{-5}\mathrm{events}/{\mathrm{keV}}_{ee}/\mathrm{kg}/\mathrm{day}$ in the low-energy region, approximately 60 times lower than the equivalent rate reported by the LUX experiment.

• Received 22 December 2022
• Accepted 30 May 2023

DOI:https://doi.org/10.1103/PhysRevD.108.012010

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Published by the American Physical Society