Migdal Effect in Dark Matter Direct Detection Experiments

TL;DR

This paper refines the theoretical understanding of the Migdal effect in dark matter detection, showing how atomic ionization during nuclear recoil can improve detection sensitivity, especially for light dark matter particles.

Contribution

It reformulates Migdal's approach to coherently calculate atomic recoil effects, clarifying energy-momentum conservation and enhancing detection prospects for light dark matter.

Findings

Ionization/excitation effects can boost light dark matter detection sensitivity.

Reformulated approach provides clearer energy-momentum conservation analysis.

Implications extend to coherent neutrino-nucleus scattering.

Abstract

The elastic scattering of an atomic nucleus plays a central role in dark matter direct detection experiments. In those experiments, it is usually assumed that the atomic electrons around the nucleus of the target material immediately follow the motion of the recoil nucleus. In reality, however, it takes some time for the electrons to catch up, which results in ionization and excitation of the atoms. In previous studies, those effects are taken into account by using the so-called Migdal's approach, in which the final state ionization/excitation are treated separately from the nuclear recoil. In this paper, we reformulate the Migdal's approach so that the "atomic recoil" cross section is obtained coherently, where we make transparent the energy-momentum conservation and the probability conservation. We show that the final state ionization/excitation can enhance the detectability of rather light dark matter in the GeV mass range via the {\it nuclear} scattering. We also discuss the coherent neutrino-nucleus scattering, where the same effects are expected.