On the Combined Analysis of Muon Shower Size and Depth of Shower Maximum

TL;DR

This paper investigates how the mean muon shower size relates to the depth of shower maximum in ultra-high energy cosmic ray air showers, enabling improved composition analysis and model comparisons.

Contribution

It provides a detailed analysis of the dependence between muon shower size and shower maximum, introducing a method to estimate primary composition and muon rescaling with high precision.

Findings

Reconstructed primary fractions differ by less than 20% across models.

Muons are rescaled by a factor with a few percent uncertainty.

Difference in muon shower size between models is about 6%.

Abstract

The mass composition of ultra-high energy cosmic rays can be studied from the distributions of the depth of shower maximum and/or the muon shower size. Here, we study the dependence of the mean muon shower size on the depth of shower maximum in detail. Air showers induced by protons and iron nuclei were simulated with two models of hadronic interactions already tuned with LHC data (run I-II). The generated air showers were combined to obtain various types of mass composition of the primary beam. We investigated the shape of the functional dependence of the mean muon shower size on the depth of shower maximum and its dependency on the composition mixture. Fitting this dependence we can derive the primary fractions and the muon rescaling factor with a statistical uncertainty at a level of few percent. The difference between the reconstructed primary fractions is below 20% when different models are considered. The difference in the muon shower size between the two models was observed to be around 6%.