Estimate of the energy spectrum of the light component of cosmic rays in HAWC using the shower age and the fraction of hit PMT's

TL;DR

This paper presents a method to estimate the energy spectrum and composition of cosmic rays using HAWC observatory data, focusing on shower age and hit PMT fraction to distinguish light components.

Contribution

The study introduces a novel analysis approach combining shower age and hit PMT fraction to improve cosmic ray composition and energy spectrum estimation at HAWC.

Findings

Effective Bayesian spectral unfolding for cosmic ray spectra.

Shower age and hit PMT fraction provide composition insights.

Light component spectrum characterized with improved accuracy.

Abstract

The High Altitude Water Cherenkov (HAWC) observatory is a ground-based air-shower detector designed to study the TeV gamma and cosmic ray windows. The observatory is composed of a densely packed array of $300$ water Cherenkov tanks, $4.5$ m deep and $7.3$ diameter with $4$ photomultipliers (PMT) each, distributed on a $22,000 \, \mbox{m}^2$ surface. The instrument registers the number of hit PMT's as well as the timing information and the total charge seen by the photomultipliers during the shower event. From the analysis of these data, shower observables such as the arrival direction, the core position at ground, the age and the primary energy are estimated, from which the energy spectrum of cosmic rays and its composition can be studied. In this work, we will describe the methodologies of HAWC cosmic ray analyses, including the Bayesian spectral unfolding procedure used to determine the all-particle and the light component energy spectra of cosmic rays. We will see that the distribution of the shower age vs the fraction of hit PMT's contains information about the composition of cosmic rays.