Study of the Cosmic Ray Composition above 0.4 EeV using the Longitudinal Profiles of Showers observed at the Pierre Auger Observatory

TL;DR

This study analyzes cosmic ray composition above 0.4 EeV using the longitudinal profiles of air showers observed at the Pierre Auger Observatory, focusing on the depth of shower maximum to infer primary particle types.

Contribution

It provides new insights into cosmic ray composition at high energies by combining fluorescence and surface detector data to measure Xmax and compare with simulation predictions.

Findings

Observed variation of <Xmax> with energy suggests a change in primary composition.

Data indicates a transition from lighter to heavier nuclei at higher energies.

Results improve understanding of cosmic ray sources and propagation.

Abstract

The Pierre Auger Observatory has been collecting data in a stable manner since January 2004. We present here a study of the cosmic ray composition using events recorded in hybrid mode during the first years of data taking. These are air showers observed by the fluorescence detector as well as the surface detector, so the depth of shower maximum, Xmax, is measured directly. The cosmic ray composition is studied in different energy ranges by comparing the observed average Xmax with predictions from air shower simulations for different nuclei. The change of <Xmax> with energy (elongation rate) is used to derive estimates of the change in primary composition.