Gamma Hadron Separation using Pairwise Compactness Method with HAWC

TL;DR

This paper introduces a novel pairwise compactness method for gamma-hadron separation in the HAWC observatory, improving background rejection by analyzing spatial hit patterns to distinguish gamma-ray events from cosmic-ray showers.

Contribution

The paper presents a new spatial relationship-based technique for primary particle identification in air showers, enhancing gamma-ray detection capabilities in ground-based observatories.

Findings

Effective gamma-ray and cosmic-ray separation demonstrated in simulations.

Improved background rejection efficiency over existing methods.

Quantitative performance metrics provided for the new technique.

Abstract

The High-Altitude Water Cherenkov (HAWC) Observatory is a ground based air-shower array deployed on the slopes of Volcan Sierra Negra in the state of Puebla, Mexico. While HAWC is optimized for the detection of gamma-ray induced air-showers, the background flux of hadronic cosmic-rays is four orders of magnitude greater, making background rejection paramount for gamma-ray observations. On average, gamma-ray and cosmic-ray showers are characterized by different topologies at ground level. We will present a method to identify the primary particle type in an air-shower that uses the spatial relationship of triggered PMTs (or "hits") in the detector. For a given event hit-pattern on the HAWC array, we calculate the mean separation distance of the hits for a subset of hit pairs weighted by their charges. By comparing the mean charge and mean separating distance for the selected hits, we infer the identity of the event's primary. We will report on the efficiency for identifying gamma-rays and the performance of the technique with simulation.