Parameterisation of lateral density and arrival time distributions of Cherenkov photons in EASs as functions of independent shower parameters for different primaries

TL;DR

This paper develops parameterisations for Cherenkov photon distributions in EASs based on simulations, aiding primary particle identification and shower reconstruction across different energies, angles, and altitudes.

Contribution

It introduces new mathematical functions to describe Cherenkov photon lateral density and arrival time distributions as functions of primary energy, angle, and altitude for different primaries.

Findings

Distributions follow specific mathematical functions with parameters varying by primary type.

Parameterisations are valid for energies from 100 GeV to 100 TeV and zenith angles up to 40°.

Distinct primaries can be identified using the derived distribution functions.

Abstract

The simulation of Cherenkov photon's lateral density and arrival time distributions in Extensive Air Showers (EASs) was performed with the CORSIKA code in the energy range: 100 GeV to 100 TeV. On the basis of this simulation we obtained a set of approximating functions for the primary $\gamma$-ray photons, protons and iron nuclei incident at zenith angles from 0$^\circ$ to 40$^\circ$ over different altitudes of observation. Such a parameterisation is important for the primary particle identification, for the reconstruction of the shower observables and hence for a more efficient disentanglement of the $\gamma$-ray showers from the hadronic showers. From our parameterisation analysis, we have found that even though the geometry of the lateral density ($\rho_{ch}$) and the arrival time ($t_{ch}$) distributions is different for different primaries at a particular energy ($E$), at a particular incident angle ($\theta$) and at a particular altitude of observation ($H$) up to a given distance from the showe core ($R$), the distributions follow the same mathematical functions $\rho(E,R,\theta,H) = a E^{b}\exp[-\{c R + (\theta /d)^{2}-f H\}]$ and $t(E,R,\theta,H) = l E^{-m}\exp(n/R^{p})({\theta}^q+s)(u {H}^2+v)$ respectively but with different values of function parameters.