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

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 $4.2\pm 0.1$ tonne-years from 280 live days of LZ operation, of which $3.3\pm 0.1$ tonne-years and 220 live days are new. A technique to actively tag background electronic recoils from ${}^{214}$Pb ${\hat{I}}^2$ 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 $\ge$9 GeV/$c^2$. The strongest SI exclusion set is $2.2\times 10^{-48}$ cm${}^2$ at the 90% confidence level and the best SI median sensitivity achieved is $5.1\times 10^{-48}$ cm${}^2$, both for a mass of 40 GeV/$c^2$.

10 pages, 7 figures. See https://www.hepdata.net/record/155182 for a data release related to this paper