Effects of Cosmic Muons on $\mu$eV-to-meV Scale Axion Dark Matter Searches

TL;DR

This study estimates cosmic muon synchrotron radiation as a potential background in axion dark matter searches, using simulations and analytical models, and finds it is not dominant currently but could affect future broadband experiments.

Contribution

It provides a combined simulation and analytical framework to evaluate cosmic muon synchrotron radiation impacts on axion searches across a wide energy range.

Findings

Cosmic muons are not the main noise source in current axion experiments due to high Q and energy resolution.

Future broadband axion experiments may be vulnerable to muon synchrotron radiation without sufficient energy resolution.

Abstract

We estimate the synchrotron radiation of cosmic muons in a uniform magnetic field in the $\mu$eV-to-meV energy scale. Such events can potentially bring backgrounds to the axion dark matter searches. The GEANT4 software package is utilized to simulate the muon tracks in a cylindrical region of interest with an 8~T solenoid magnetic field applied. We further develop an analytical estimation of the angular-frequency-differential synchrotron radiation power spectra in this work as the cosmic muons span a wide range of Lorentz factor $\gamma$ and pitch angle $\alpha$. We verify that the cosmic muons are not the dominant noise background for the current axion dark matter experiments on the $\mu$eV scale because of the high quality factor $Q$ and fine energy resolution in the readout. However, without sufficient energy resolution in the detector readout, future broadband axion dark matter experiments will be vulnerable to the synchrotron radiation of these charged particles.