Confronting the Higgsino Interpretation of the LZ Event with Astrophysical Uncertainties and the Solar Capture Constraints

We investigate whether astrophysical uncertainties in the local dark matter distribution can alleviate tensions between the higgsino interpretation of the LZ event and constraints from solar-capture neutrinos. We calculate the expected LZ signal over a wide range of Standard Halo Model parameters and using $N$-body hydrodynamical simulations of Milky Way-like galaxies that include the influence of the Large Magellanic Cloud. For the Standard Halo Model, the requirement $\delta \gtrsim 566\mathrm{k}\mathrm{e}\mathrm{V}$ implies $v_0\gtrsim 240\mathrm{k}\mathrm{m}{\mathrm{s}}^{-1}$, independent of the Galactic escape speed. In the simulated halo, we find that $\delta =514\mathrm{k}\mathrm{e}\mathrm{V}$ is the largest mass splitting capable of producing one event in LZ’s $200\mathrm{k}\mathrm{e}\mathrm{V}-300\mathrm{k}\mathrm{e}\mathrm{V}$ recoil-energy range. We conclude that astrophysical uncertainties are insufficient to reconcile the higgsino interpretation of the LZ event with solar-capture neutrino constraints.