The knee in the cosmic ray energy spectrum from the simultaneous EAS charged particles and muon density spectra

TL;DR

This study uses Monte Carlo simulations to analyze cosmic ray air shower data, revealing that a consistent primary energy spectrum with a knee feature depends on the assumed primary composition, especially whether it remains constant or changes across the knee.

Contribution

It demonstrates that the primary cosmic ray spectrum's knee feature can be inferred from EAS data only under specific composition assumptions, highlighting the complexity of spectrum estimation.

Findings

A pure iron primary composition suggests a knee in the spectrum.

No consistent spectrum is found when combining KASCADE data without composition assumptions.

Estimating the spectral index near the knee is sensitive to data selection and composition assumptions.

Abstract

In this work we examine with the help of Monte Carlo simulation whether a consistent primary energy spectrum of cosmic rays emerges from both the experimentally observed total charged particles and muon size spectra of cosmic ray extensive air showers considering primary composition may or may not change beyond the knee of the energy spectrum. It is found that EAS-TOP observations consistently infer a knee in the primary energy spectrum provided the primary is pure unchanging iron whereas no consistent primary spectrum emerges from simultaneous use of the KASCADE observed total charged particle and muon spectra. However, it is also found that when primary composition changes across the knee the estimation of spectral index of total charged particle spectrum is quite tricky, depends on the choice of selection of points near the knee in the size spectrum.