Exploring light dark matter with the Migdal effect in hydrogen-doped liquid xenon

Abstract

An ongoing challenge in dark matter direct detection is to improve the sensitivity to light dark matter in the MeV–GeV mass range. One proposal is to dope a liquid noble-element direct-detection experiment with a lighter element such as hydrogen. This has the advantage of enabling larger recoil energies compared to scattering on a heavy target, while leveraging existing detector technologies. Direct-detection experiments can also extend their reach to lower masses by exploiting the Migdal effect, where a nuclear recoil leads to electronic ionization or excitation. In this work, we combine these ideas to study the sensitivity of a hydrogen-doped LZ experiment (HydroX) and a future large-scale experiment such as XLZD. We find that HydroX could have sensitivity to dark matter masses below 10 MeV for both spin-independent and spin-dependent scattering, with XLZD extending that reach to lower cross sections. Notably, this technique substantially enhances the sensitivity of direct detection to spin-dependent proton scattering, well beyond the reach of any current experiments. Published by the American Physical Society 2024