Search for seasonal variations of the horizontal muon rate with the HAWC observatory

TL;DR

This study investigates seasonal variations in the horizontal muon rate using 1.5 years of HAWC data, introducing a new method to analyze effective temperature effects on muons at high altitude.

Contribution

First to report seasonal variations in high-altitude horizontal muon rates and develop a method to calculate effective temperature for horizontal muon propagation.

Findings

Detected seasonal variations in horizontal muon rate.

Established a correlation between effective temperature and muon rate.

Developed a novel method for effective temperature calculation for horizontal muons.

Abstract

The High-Altitude Water Cherenkov (HAWC) observatory was designed to study gamma-ray sources in the energy range between a few hundred GeV up to few hundred TeV. It is composed of 300 Water Cherenkov Detectors (WCDs) that cover a surface of approximately 22000 m${}^2$, at 4100 m a.s.l. In this study, we use the HAWC WCDs as a very large horizontal particle tracker, searching for horizontal muon rate variations by season using 1.5 years of HAWC data. We look for a possible correlation between the effective temperature and the horizontal muon rate. In order to do this, we developed a method to calculate the effective temperature for the horizontal propagation of muons. This is the first time that a search for seasonal variations in the high-altitude horizontal muon rate is reported.