Dark Matter Search Results from 4.2 Tonne-Years of Exposure of the LUX-ZEPLIN (LZ) Experiment

TL;DR

This paper reports the results of a dark matter search using the LUX-ZEPLIN detector with 4.2 tonne-years of data, setting world-leading limits on WIMP interactions and introducing new background tagging techniques.

Contribution

The study presents the first use of active background tagging in LZ data and reports enhanced electron-ion recombination in xenon, improving background understanding.

Findings

No excess events observed over background expectations.

Set the most stringent limits on WIMP-nucleon cross sections for masses ≥9 GeV/c².

Achieved the best median sensitivity of 5.1×10⁻⁴⁸ cm² at 40 GeV/c².

Abstract

We report results of a search for nuclear recoils induced by weakly interacting massive particle (WIMP) dark matter using the LUX-ZEPLIN (LZ) two-phase xenon time projection chamber. This analysis uses a total exposure of $4.2\pm0.1$ tonne-years from 280 live days of LZ operation, of which $3.3\pm0.1$ tonne-years and 220 live days are new. A technique to actively tag background electronic recoils from $^{214}$Pb $\beta$ decays is featured for the first time. Enhanced electron-ion recombination is observed in two-neutrino double electron capture decays of $^{124}$Xe, representing a noteworthy new background. After removal of artificial signal-like events injected into the data set to mitigate analyzer bias, we find no evidence for an excess over expected backgrounds. World-leading constraints are placed on spin-independent (SI) and spin-dependent WIMP-nucleon cross sections for masses $\geq$9 GeV/$c^2$. The strongest SI exclusion set is $2.2\times10^{-48}$ cm$^{2}$ at the 90% confidence level and the best SI median sensitivity achieved is $5.1\times10^{-48}$ cm$^{2}$, both for a mass of 40 GeV/$c^2$.