Extensive Air Shower Universality of Ground Particle Distributions

The number and the energy and angular distributions of particles in extensive air showers depend on the stage of the shower development and the distance to the shower axis. In this work we derive an analytic parameterization of the particle distributions at ground from air shower simulations. Shower partic les are classified in four components according to the shower component they belong to and the transverse momentum of the last hadronic interaction of their production. Using this scheme, we will show that the total signal at ground level can be described with universal parametrizations in dependence on the primary energy, position of the shower maximum, and the overall number of muons in the shower. The simulation results are reproduced with an accuracy of 5-10% in the range from 100 to 2000 m from the shower core. The differences between hadronic models and primaries are only due to the different predictions of these quantities. The truncation of the shower development due to the presence of the ground is taken into account and effects due to the geometry of possible surface detectors are outlined.