Higgsino Dark Matter Interpretation of the LUX-ZEPLIN 248 keV Nuclear-Recoil Event

We propose Higgsino dark matter as a potential interpretation of the $248\mathrm{k}\mathrm{e}\mathrm{V}$ nuclear-recoil event of interest reported by the LUX-ZEPLIN (LZ) experiment. LZ studied several rare background processes and detector effects in detail, but did not identify any as a likely explanation of the event. A nearly pure Higgsino with mass $m_{\tilde{H}}\sim 1\mathrm{T}\mathrm{e}\mathrm{V}$ naturally realizes inelastic dark matter through the off-diagonal $Z$ coupling of two nearly degenerate neutral Majorana states separated by a mass splitting $\delta$. The same electroweak interaction fixes the inelastic Higgsino-nucleon scattering cross section, rather than leaving it as a free parameter. We show that the predicted Higgsino inelastic scattering cross section approaches the published LZ two-sided 90% confidence interval for $\delta \sim 350\mathrm{k}\mathrm{e}\mathrm{V}$.