Muon content of ultra-high-energy air showers: Yakutsk data versus simulations

TL;DR

This study compares observed muon densities in ultra-high-energy air showers with simulations to infer primary cosmic ray composition, revealing a mixed proton-iron composition and model-dependent differences.

Contribution

It provides a detailed event-by-event comparison of muon data with simulations using different hadronic models, highlighting composition insights and model discrepancies.

Findings

EPOS model aligns well with a mixed proton-iron composition.

SIBYLL underestimates muon densities for iron primaries.

Proton fraction above 10^{19} eV is approximately 52%.

Abstract

We analyse a sample of 33 extensive air showers (EAS) with estimated primary energies above 2\cdot 10^{19} eV and high-quality muon data recorded by the Yakutsk EAS array. We compare, event-by-event, the observed muon density to that expected from CORSIKA simulations for primary protons and iron, using SIBYLL and EPOS hadronic interaction models. The study suggests the presence of two distinct hadronic components, ``light'' and ``heavy''. Simulations with EPOS are in a good agreement with the expected composition in which the light component corresponds to protons and the heavy component to iron-like nuclei. With SYBILL, simulated muon densities for iron primaries are a factor of \sim 1.5 less than those observed for the heavy component, for the same electromagnetic signal. Assuming two-component proton-iron composition and the EPOS model, the fraction of protons with energies E>10^{19} eV is 0.52^{+0.19}_{-0.20} at 95% confidence level.