A phenomenological model of the muon density profile on the ground of very inclined air showers

TL;DR

This paper introduces a phenomenological model for the muon density profile in very inclined air showers, enabling accurate and efficient reconstruction of ultra-high energy cosmic ray events from ground-based measurements.

Contribution

It presents a new parametrization scheme derived from Monte Carlo simulations that accurately models muon density profiles for inclined air showers, improving reconstruction speed and precision.

Findings

Model reproduces detailed simulations with high accuracy

Valid for energies 10^18 to 10^20 eV and zenith angles 60° to 90°

Speeds up muon profile simulations by three orders of magnitude

Abstract

Ultra-high energy cosmic rays generate extensive air showers in Earth's atmosphere. A standard approach to reconstruct the energy of an ultra-high energy cosmic rays is to sample the lateral profile of the particle density on the ground of the air shower with an array of surface detectors. For cosmic rays with large inclinations, this reconstruction is based on a model of the lateral profile of the muon density observed on the ground, which is fitted to the observed muon densities in individual surface detectors. The best models for this task are derived from detailed Monte-Carlo simulations of the air shower development. We present a phenomenological parametrization scheme which allows to derive a model of the average lateral profile of the muon density directly from a fit to a set of individual Monte-Carlo simulated air showers. The model reproduces the detailed simulations with a high precision. As an example, we generate a muon density model which is valid in the energy range 1e18 eV < E < 1e20 eV and the zenith angle range 60 deg < theta < 90 deg. We will further demonstrate a way to speed up the simulation of such muon profiles by three orders of magnitude, if only the muons in the shower are of interest.