Measurements of the Cosmic Ray Composition with Air Shower Experiments

TL;DR

This paper reviews methods and results from air shower experiments to determine the composition of cosmic rays above 10^15 eV, highlighting the challenges and uncertainties in interpreting the data.

Contribution

It provides a comprehensive overview of composition measurement techniques and compares results across different models and detectors in cosmic ray research.

Findings

Cosmic ray composition becomes lighter at higher energies.

Different hadronic interaction models yield varying mass estimates.

Air shower observables are sensitive to primary mass and energy.

Abstract

In this paper we review air shower data related to the mass composition of cosmic rays above 10$^{15}$ eV. After explaining the basic relations between air shower observables and the primary mass and energy of cosmic rays, we present different approaches and results of composition studies with surface detectors. Furthermore, we discuss measurements of the longitudinal development of air showers from non-imaging Cherenkov detectors and fluorescence telescopes. The interpretation of these experimental results in terms of primary mass is highly susceptible to the theoretical uncertainties of hadronic interactions in air showers. We nevertheless attempt to calculate the logarithmic mass from the data using different hadronic interaction models and to study its energy dependence from 10$^{15}$ to 10$^{20}$ eV.