Flow-dependent tagging of $^{214}$Pb decays in the LZ dark matter detector

TL;DR

This paper presents a flow-dependent tagging method in the LZ dark matter detector that identifies $^{214}$Pb decays by tracking fluid flow and ion drift, improving background discrimination in the search for dark matter.

Contribution

It introduces a novel flow-based tagging technique for $^{214}$Pb decays in a liquid xenon detector, enhancing background identification without interrupting science data collection.

Findings

Achieved 63% identification efficiency of $^{214}$Pb decays.

Mapped fluid flow and ion drift in the detector.

Enabled a new calibration method concurrent with data collection.

Abstract

The LUX-ZEPLIN (LZ) experiment is searching for dark matter interactions in a liquid xenon time projection chamber (LXe-TPC). This article demonstrates how control of the flow state in the LXe-TPC enables the identification of pairs of sequential alpha-decays, which are used to map fluid flow and ion drift in the liquid target. The resulting transport model is used to tag $^{214}$Pb beta-decays, a leading background to dark matter signals in LZ. Temporally evolving volume selections, at a cost of 9.0% of exposure, target the decay of each $^{214}$Pb atom up to 81 minutes after production, resulting in (63 $\pm$ 6$_{\mathrm{stat}}$ $\pm$ 7$_{\mathrm{sys}}$)% identification of $^{214}$Pb decays to ground state. We also demonstrate how flow-based tagging techniques enable a novel calibration side band that is concurrent with science data.