Studying the nuclear mass composition of Ultra-High Energy Cosmic Rays with the Pierre Auger Observatory

TL;DR

This paper analyzes the nuclear mass composition of ultra-high energy cosmic rays using data from the Pierre Auger Observatory, comparing measurements with theoretical models to understand cosmic ray origins.

Contribution

It provides new measurements of $X_{max}$ distributions and composition-sensitive parameters, enhancing understanding of cosmic ray mass composition at ultra-high energies.

Findings

$X_{max}$ distributions vary with energy and are compared to model predictions.

Ground-level composition-sensitive parameters are analyzed.

Results suggest specific nuclear mass compositions at different energies.

Abstract

The Fluorescence Detector of the Pierre Auger Observatory measures the atmospheric depth, $X_{max}$, where the longitudinal profile of the high energy air showers reaches its maximum. This is sensitive to the nuclear mass composition of the cosmic rays. Due to its hybrid design, the Pierre Auger Observatory also provides independent experimental observables obtained from the Surface Detector for the study of the nuclear mass composition. We present $X_{max}$-distributions and an update of the average and RMS values in different energy bins and compare them to the predictions for different nuclear masses of the primary particles and hadronic interaction models. We also present the results of the composition-sensitive parameters derived from the ground level component.