Measurement of the chemical composition of the ultra-high-energy cosmic rays with the Pierre Auger Observatory

TL;DR

This paper reports on the measurement of ultra-high-energy cosmic ray composition using the Pierre Auger Observatory's fluorescence and surface detectors, analyzing data for energies above 10^18 eV and comparing results with theoretical models.

Contribution

It provides new measurements of cosmic ray composition using dual detection methods and compares these with predictions from various hadronic interaction models.

Findings

Distribution of $X_{max}$ analyzed for energies above 10^18 eV

Mass composition results suggest a mixed or evolving composition at ultra-high energies

Comparison with proton and iron models highlights model-dependent interpretations

Abstract

The Pierre Auger Observatory infers the chemical composition of ultra-high-energy cosmic rays through two independent detection techniques. The Fluorescence Detector (FD) measures the longitudinal profile of high energy air showers and can determine the depth of the shower maximum $X_{max}$, which is sensitive to the chemical composition of the primary cosmic rays. Additionally, measurements by the Surface Detector (SD) provide independent experimental observables based on the muonic shower component to analyze the chemical composition. We present the results for the $X_{max}$ distributions and the mass composition results measured by the FD and the SD for the energies $E \geq 10^{18}$\,eV. The data will be compared with the expectations for proton and iron primaries according to different hadronic interaction models.