Muons as a tool for background rejection in Imaging Atmospheric Cherenkov Telescope arrays

TL;DR

This paper investigates using Cherenkov light from muons in air showers as a method to significantly reduce background noise in high-energy gamma-ray observations with large imaging atmospheric Cherenkov telescopes.

Contribution

It introduces an analytical model for muon Cherenkov light, enabling rapid simulations and demonstrating potential for high background rejection efficiency in large telescope arrays.

Findings

Background rejection up to 10^-5 with large telescopes

Effective muon identification can improve gamma-ray detection

Feasibility shown for arrays with at least one large telescope

Abstract

The presence of muons in air-showers initiated by cosmic ray protons and nuclei is well established as a powerful tool to separate such showers from those initiated by gamma rays. However, so far this approach has been fully exploited only for ground level particle detecting arrays. We explore the feasibility of using Cherenkov light from muons as a background rejection tool for imaging atmospheric Cherenkov telescope arrays at the highest energies. We adopt an analytical model of the Cherenkov light from individual muons to allow rapid simulation of a large number of showers in a hybrid mode. This allows us to explore the very high background rejection power regime at acceptable cost in terms of computing time. We show that for very large ($\gtrsim$20 m mirror diameter) telescopes, efficient identification of muon light can potentially lead to background rejection levels up to 10$^{-5}$ whilst retaining high efficiency for gamma rays. While many challenges remain in the effective exploitation of the muon Cherenkov light in the data analysis for imaging Cherenkov telescope arrays, our study indicates that for arrays containing at least one large telescope, this is a very worthwhile endeavor.