Dark matter implications from the XENONnT and LZ data

TL;DR

This study explores dark matter explanations for high-energy recoil events in XENONnT and LZ data, using a unified framework to fit multiple datasets and considering velocity-dependent and inelastic interactions, with implications for future high-energy analyses.

Contribution

First combined profile-likelihood analysis of XENONnT and LZ data addressing high-energy recoil events with novel dark matter interaction models.

Findings

Velocity-dependent and inelastic dark matter interactions can explain high-energy recoil spectrum.

Significance of dark matter interpretation varies from below 1σ to 4σ depending on background assumptions.

Future high-energy data will be crucial for testing the dark matter hypothesis.

Abstract

We investigate a possible dark matter origin of the high-energy nuclear-recoil-like events in XENONnT and LZ data, which cannot be explained by standard elastic spin-independent WIMP scattering. Using our unified DIAMX framework, built on openly available data and likelihood models, we perform the first combined profile-likelihood fits to multiple WIMP-search datasets with a total exposure of 7.3 tonne$\times$year. We investigate that two broad classes of dark matter nucleon interactions, with velocity-dependent cross-section or inelastic (endo- and exothermic) scattering, can reproduce the observed high-energy recoil spectrum, reaching local significances up to $4\sigma$. We further quantify the impact of $^{124}$Xe double electron capture (DEC) backgrounds, finding that variations in the poorly known DEC charge yields can shift the inferred significances from below $1\sigma$ to $4\sigma$. We point out that extending the same analysis to XENONnT and LZ data with recoil energies up to 300 keV, once available, will provide a powerful test of the dark matter interpretation, since the $^{124}$Xe DEC background is expected to be negligible in this high-energy range.