Galactic Endothermic Production and Exothermic Detection of Excited Dark Matter: Implications for LUX-ZEPLIN

Abstract

The LUX-ZEPLIN experiment reported a candidate nuclear recoil at $248\,\mathrm{keV}$. This work proposes that endothermic self-scattering $χ_1χ_1\toχ_2χ_2$ in the Galaxy can produce an excited dark matter population, whose exothermic scattering $χ_2 A\toχ_1 A$ in xenon can account for the LZ candidate event. In a benchmark with a light scalar mediator, the conversion cross section is large enough for high-velocity Galactic dark matter particles to generate an excited fraction at the percent level. For dark matter masses near the TeV scale and splittings below $1\,\mathrm{MeV}$, the xenon recoil spectrum covers the candidate region and can yield an $\mathcal O(1)$ event count.