Modulation Effects in Dark Matter-Electron Scattering Experiments

TL;DR

This paper develops a semi-analytic method to better understand dark matter-electron scattering signals in direct detection experiments, focusing on their time-dependent modulation and Earth-induced distortions for sub-GeV dark matter.

Contribution

It introduces a semi-analytic approach to accurately model electron scattering in atomic and semiconductor targets, improving signal predictions over previous methods.

Findings

Enhanced modeling of electron recoil signals at high energies.

Identification of unique time-dependent modulation patterns.

Demonstration of Earth effects on dark matter phase-space distribution.

Abstract

One of the next frontiers in dark-matter direct-detection experiments is to explore the MeV to GeV mass regime. Such light dark matter does not carry enough kinetic energy to produce an observable nuclear recoil, but it can scatter off electrons, leading to a measurable signal. We introduce a semi-analytic approach to characterize the resulting electron-scattering events in atomic and semiconductor targets, improving on previous analytic proposals that underestimate the signal at high recoil energies. We then use this procedure to study the time-dependent properties of the electron-scattering signal, including the modulation fraction, higher-harmonic modes and modulation phase. The time dependence can be distinct in a non-trivial way from the nuclear scattering case. Additionally, we show that dark-matter interactions inside the Earth can significantly distort the lab-frame phase-space distribution of sub-GeV dark matter.