Anisotropic ionization threshold and directional sensitivity in solid state DM detectors

TL;DR

This paper investigates how the directional dependence of ionization thresholds in solid-state dark matter detectors causes daily modulation in event rates, offering a method to distinguish dark matter signals from neutrino backgrounds.

Contribution

It introduces the concept of anisotropic ionization thresholds affecting low-energy nuclear recoils and explores their implications for dark matter detection strategies.

Findings

Directional dependence causes daily modulation in event rates.

Modulation pattern helps differentiate dark matter signals from neutrino background.

Structure of modulation reveals information about DM-nucleon coupling.

Abstract

The threshold displacement energy for nuclear recoils depends strongly on the direction of the recoiling nucleus with respect to the crystal lattice. Assuming that similar dependence holds for the ionization threshold for low energy nuclear recoils, we explore the consequences of the resulting directional dependence of the observable event rate in ionization detectors. For low mass dark matter, this effect leads to a daily modulation in the event rate. We discuss how this effect can be utilized to separate the DM signal from the solar neutrino background and how the structure of the modulation signal can be used to identify the type of the DM-nucleon coupling.