Discarded low energy particles in extensive air shower simulations: Effect on the shower Missing and Invisible Energy

Abstract

The energy carried away by neutral particles in ultra high energy cosmic ray showers can not be detected by fluorescence detectors. This energy is usually referred to as the "invisible energy". Since every shower has a fraction of invisible energy, the energy determined using the fluorescence technique is always less than the primary energy and a correction needs to be applied. This correction, usually referred to as the "missing energy", can only be estimated using Monte Carlo simulations. In this article we study in detail the influence that discarding low energy particles from the simulation has on the estimation of the missing and invisible energies. We found that although the effect is not important for the invisible energy,an important bias on the missing energy is introduced that can reach 30% or more depending on the low energy cut value. We present a prescription on how to correct for this bias in AIRES simulations and give a novel missing energy parametrization including results for photons and for the QGSJET-II hadronic model. We also show that although missing and invisible energies are closely related they are conceptually different ideas if we consider the medium contribution to the shower energy.