The Lateral Trigger Probability function for the Ultra-High Energy Cosmic Ray Showers detected by the Pierre Auger Observatory

TL;DR

This paper introduces the Lateral Trigger Probability function for ultra-high energy cosmic ray showers, modeling detector trigger likelihood based on shower parameters, validated through simulations and hybrid data from the Pierre Auger Observatory.

Contribution

It presents a new probabilistic model for detector triggering in cosmic ray arrays, incorporating energy, mass, and direction, validated with Monte Carlo simulations and hybrid observational data.

Findings

LTP functions are well described by a combined step and exponential model.

Monte Carlo simulations agree with hybrid observational data.

LTP functions effectively characterize detector response across energies and angles.

Abstract

In this paper we introduce the concept of Lateral Trigger Probability (LTP) function, i.e., the probability for an extensive air shower (EAS) to trigger an individual detector of a ground based array as a function of distance to the shower axis, taking into account energy, mass and direction of the primary cosmic ray. We apply this concept to the surface array of the Pierre Auger Observatory consisting of a 1.5 km spaced grid of about 1600 water Cherenkov stations. Using Monte Carlo simulations of ultra-high energy showers the LTP functions are derived for energies in the range between 10^{17} and 10^{19} eV and zenith angles up to 65 degs. A parametrization combining a step function with an exponential is found to reproduce them very well in the considered range of energies and zenith angles. The LTP functions can also be obtained from data using events simultaneously observed by the fluorescence and the surface detector of the Pierre Auger Observatory (hybrid events). We validate the Monte-Carlo results showing how LTP functions from data are in good agreement with simulations.