Light Dark Matter Search with 7.8 Tonne-Year of Ionization-Only Data in XENONnT

TL;DR

This paper reports on a sensitive search for light dark matter using ionization signals in XENONnT, setting new upper limits on various dark matter interactions with nuclei and electrons, and improving constraints over previous experiments.

Contribution

First complete S2-only background model in XENONnT enabling sensitive searches for low-mass dark matter particles.

Findings

No significant excess observed over background.

Set new upper limits on spin-independent DM-nucleon cross sections.

Excluded cross sections above 6.0×10⁻⁴⁵ cm² at 5 GeV/c² DM mass.

Abstract

We report on a blinded search for dark matter (DM) using ionization-only (S2-only) signals in XENONnT with a total exposure of $7.83\mathrm{tonne}\times\mathrm{year}$ over 579 days in three science runs. Dedicated background suppression techniques and the first complete S2-only background model in XENONnT provide sensitivity to nuclear recoils of [0.5, 5.0] $\mathrm{keV_\mathrm{nr}}$ and electronic recoils of [0.04, 0.7] $\mathrm{keV_\mathrm{ee}}$. No significant excess over the expected background is observed, and we set 90\% confidence level upper limits on spin-independent DM--nucleon and spin-dependent DM--neutron scattering for DM masses between 3 and 8 $\mathrm{GeV}/c^2$, as well as on DM--electron scattering, axion-like particles, and dark photons, improving on previous constraints. For spin-independent DM--nucleon scattering, we exclude cross sections above $6.0\times10^{-45} $cm$^2$ at a DM mass of 5 $\mathrm{GeV}/c^2$, pushing the XENONnT sensitivity closer to the region where coherent elastic neutrino-nucleus scattering ($\text{CE}\nu\text{NS}$) becomes an irreducible background.