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

The LUX-ZEPLIN experiment reported a candidate nuclear recoil at $248\mathrm{k}\mathrm{e}\mathrm{V}$. This work proposes that endothermic self-scattering ${\chi }_1{\chi }_1\to {\chi }_2{\chi }_2$ in the Galaxy can produce an excited dark matter population, whose exothermic scattering ${\chi }_{2}A\to {\chi }_{1}A$ 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 $1\mathrm{M}\mathrm{e}\mathrm{V}$, the xenon recoil spectrum covers the candidate region and can yield an $\mathcal{O}(1)$ event count.