Muon lateral distribution function of extensive air showers: results of the Sydney University Giant Air-shower Recorder versus modern Monte-Carlo simulations

TL;DR

This study compares empirical muon density distributions from the SUGAR air-shower array with modern simulations, revealing a faster fall-off in observed muon densities than predicted, which impacts understanding of the muon excess in cosmic ray physics.

Contribution

It provides the first empirical muon lateral distribution function from SUGAR data and compares it with state-of-the-art hadronic interaction models, highlighting discrepancies.

Findings

Observed muon densities decrease faster than simulations predict.

Discrepancies may influence interpretations of the muon excess.

Results suggest potential refinements needed in hadronic interaction models.

Abstract

The Sydney University Giant Air-shower Recorder (SUGAR) measured the muon component of extensive air showers with a unique array of muon detectors. The SUGAR data allow us to reconstruct the empirical dependence of muon density on the distance from the axis of the shower, the lateral distribution function (LDF). We compare the shape of this function with the predictions of hadronic-interaction models, QGSJET-II-04 and EPOS-LHC, in the energy range 10^17.6 - 10^18.6 eV. We find a difference between the observed data and the simulation: the observed muon density falls faster with the increased core distance than it is predicted in simulations. This observation may be important for interpretation of the energy-dependent discrepancies in the simulated and observed numbers of muons in air showers, known as the "muon excess".