Muons in EAS with E>=10^17eV according to the data from Yakutsk array

TL;DR

This study analyzes muon distributions in ultra-high-energy cosmic ray showers using Yakutsk array data, comparing observations with simulations to infer cosmic ray composition at different energies.

Contribution

It provides the first detailed comparison of muon lateral distributions with various hadron interaction models, identifying QGSJETII-04 as the best fit and estimating cosmic ray composition changes.

Findings

Best agreement with QGSJETII-04 model

Mixed composition at 10^17 eV with <lnA>~3.0

Lighter composition at energies above 4*10^17 eV with <lnA>~0.5

Abstract

The lateral distribution of muons with threshold energy e ~ 1*sec(theta) GeV have been studied in showers with energy E>=10^17 eV. The data considered in the analysis have been collected from November 2011 to June 2013. Experimental values are compared to predictions obtained with the use of CORSIKA code within the framework of various hadron interaction models. The best agreement between experiment and theory is observed for QGSJETII-04 model. At E~10^17 eV it complies to a mixed cosmic ray composition with the mean atomic number <lnA>~3.0+/-0.5. At E>= 4*10^17 eV the composition varies around the value <lnA>~0.5.