Inelastic Dark Matter Signature at High Recoil Energy in LUX-ZEPLIN and CRESST

Abstract

The LUX--ZEPLIN Collaboration recently reported one event at $E_{\mathrm{nr}}=248\pm 23\mathrm{keV}$ with an exposure of $2.84\mathrm{tonne}\cdot \mathrm{yr}$. In this Letter, we interpret this feature using endothermic dark matter (DM). We consider both direct scattering of the surviving ground-state halo component and the contribution of excited states produced by terrestrial upscattering. Our calculations show that explaining the high-energy event requires $m_{\chi }\gtrsim 500\mathrm{GeV}$ and a mass splitting of $\mathcal{O}(300)\mathrm{keV}$, for which the production of excited states inside the Earth is kinematically forbidden. For ${\bar{\sigma }}_n=10^{-37}\mathrm{c}{\mathrm{m}}^2$, an illustrative two-bin likelihood analysis yields a representative best-fit point at $(m_{\chi },\delta )\simeq (1.105\mathrm{TeV},350\mathrm{keV})$. The preferred parameter region may be tested by the planned CRESST upgrade.

Comments: 7 pages, 4 figures