# Average shape of longitudinal shower profiles measured at the Pierre Auger Observatory

## TL;DR

This study measures the average longitudinal shower profiles of cosmic rays at the Pierre Auger Observatory, confirming model predictions and providing insights into high-energy cosmic ray interactions.

## Contribution

First measurement of average cosmic ray shower profiles using Fluorescence Detectors at Pierre Auger Observatory, with detailed shape analysis and model comparison.

## Key findings

- Profiles are well fitted by Gaisser-Hillas parametrization within 1%
- Shape parameters are consistent with model predictions within uncertainties
- Systematic uncertainties limit detailed cosmic ray composition analysis

## Abstract

The average profiles of cosmic ray shower development as a function of atmospheric depth are measured for the first time with the Fluorescence Detectors at the Pierre Auger Observatory. The profile shapes are well reproduced by the Gaisser-Hillas parametrization at the 1% level in a 500 g/cm2 interval around the shower maximum, for cosmic rays with log(E/eV) > 17.8. The results are quantified with two shape parameters, measured as a function of energy. The average profiles carry information on the primary cosmic ray and its high energy hadronic interactions. The shape parameters predicted by the commonly used models are compatible with the measured ones within experimental uncertainties. Those uncertainties are dominated by systematics which, at present, prevent a detailed composition analysis.