Directional Detectability of Dark Matter With Single Phonon Excitations: Target Comparison

TL;DR

This paper compares 26 crystal targets for detecting light dark matter via single phonon excitations, emphasizing the importance of anisotropy and daily modulation signals to enhance detection sensitivity.

Contribution

It provides a detailed comparative analysis of crystal targets, identifying optimal materials like sapphire, CaWO4, and h-BN for observing daily modulation in dark matter detection.

Findings

Al₂O₃, CaWO₄, and h-BN show strong daily modulation signals.

Directional detection helps mitigate backgrounds.

Modulation amplitudes can reach up to 100% depending on parameters.

Abstract

Single phonon excitations are sensitive probes of light dark matter in the keV-GeV mass window. For anisotropic target materials, the signal depends on the direction of the incoming dark matter wind and exhibits a daily modulation. We discuss in detail the various sources of anisotropy, and carry out a comparative study of 26 crystal targets, focused on sub-MeV dark matter benchmarks. We compute the modulation reach for the most promising targets, corresponding to the cross section where the daily modulation can be observed for a given exposure, which allows us to combine the strength of DM-phonon couplings and the amplitude of daily modulation. We highlight Al$_2$O$_3$ (sapphire), CaWO$_4$ and h-BN (hexagonal boron nitride) as the best polar materials for recovering a daily modulation signal, which feature $\mathcal{O}(1 - 100)\%$ variations of detection rates throughout the day, depending on the dark matter mass and interaction. The directional nature of single phonon excitations offers a useful handle to mitigate backgrounds, which is crucial for fully realizing the discovery potential of near future experiments.