Interpretation of the Depths of Maximum of Extensive Air Showers Measured by the Pierre Auger Observatory

TL;DR

This paper presents a method to interpret the depth of maximum of cosmic ray air showers using parametrization of the first two moments of the $ ext{ln}A$ distribution, applied to Pierre Auger Observatory data to study cosmic ray composition.

Contribution

The paper introduces a simple parametrization method to interpret the depth of maximum and its dispersion in cosmic ray air showers, linking it to the $ ext{ln}A$ distribution and applying it to observational data.

Findings

Energy dependence of mean $ ext{ln}A$ observed

Variance of $ ext{ln}A$ analyzed under different models

Implications for cosmic ray sources discussed

Abstract

To interpret the mean depth of cosmic ray air shower maximum and its dispersion, we parametrize those two observables as functions of the first two moments of the $\ln A$ distribution. We examine the goodness of this simple method through simulations of test mass distributions. The application of the parameterization to Pierre Auger Observatory data allows one to study the energy dependence of the mean $\ln A$ and of its variance under the assumption of selected hadronic interaction models. We discuss possible implications of these dependences in term of interaction models and astrophysical cosmic ray sources.