Migdal effect and photon Bremsstrahlung: improving the sensitivity to light dark matter of liquid argon experiments

TL;DR

This paper explores how Migdal electrons and Bremsstrahlung photons can enhance liquid argon detectors' sensitivity to light dark matter particles down to 0.1 GeV/c^2, using Bayesian analysis and simulations inspired by DarkSide-50.

Contribution

It introduces a Bayesian method to incorporate Migdal and Bremsstrahlung effects, extending dark matter search sensitivity to lower masses in liquid argon detectors.

Findings

Migdal and Bremsstrahlung effects can significantly improve sensitivity.

Sensitivity can reach down to 0.1 GeV/c^2 dark matter mass.

Earth shielding impacts detection of strongly interacting dark matter.

Abstract

The search for dark matter weakly interacting massive particles with noble liquids has probed masses down and below a GeV/c^2. The ultimate limit is represented by the experimental threshold on the energy transfer to the nuclear recoil. Currently, the experimental sensitivity has reached a threshold equivalent to a few ionization electrons. In these conditions, the contribution of a Bremsstrahlung photon or a so-called Migdal electron due to the sudden acceleration of a nucleus after a collision might be sizable. In the present work, we use a Bayesian approach to study how these effects can be exploited in experiments based on liquid argon detectors. In particular, taking inspiration from the DarkSide-50 public spectra, we develop a simulated experiment to show how the Migdal electron and the Bremsstrahlung photon allow to push the experimental sensitivity down to masses of 0.1 GeV/c^2, extending the search region for dark matter particles of previous results. For these masses we estimate the effect of the Earth shielding that, for strongly interacting dark matter, makes any detector blind. Finally, we show how the sensitivity scales for higher exposure.