Daily modulation of low-energy nuclear recoils from sub-GeV dark matter

TL;DR

This paper calculates the daily modulation of low-energy nuclear recoils caused by sub-GeV dark matter in anisotropic crystals, revealing potential for directional detection through phonon excitations.

Contribution

It extends previous models by calculating multiphonon daily modulation in anisotropic crystals, implementing the results in the DarkELF package, and exploring a wider dark matter mass range.

Findings

Modulation rates up to 10% for Al₂O₃ with DM below 30 MeV.

Similar modulation results for SiC.

Negligible modulation in Si, GaAs, and SiO₂.

Abstract

At sufficiently low nuclear recoil energy, the scattering of dark matter (DM) in crystals gives rise to single phonon and multiphonon excitations. In anisotropic crystals, the scattering rate into phonons modulates over each sidereal day as the crystal rotates with respect to the DM wind. This gives a potential avenue for directional detection of DM. The daily modulation for single phonons has previously been calculated. Here we calculate the daily modulation for multiphonon excitations from DM in the mass range 1 MeV-1 GeV. We generalize previous multiphonon calculations, which made an isotropic approximation, and implement results in the DarkELF package. We find daily modulation rates up to 1-10 percent for an Al$_2$O$_3$ target and DM mass below 30 MeV, depending on the recoil energies probed. We obtain similar results for SiC, while modulation in Si, GaAs and SiO$_2$ is negligible.