Superposition model test in small CORSIKA shower simulations

Abstract: The calculation of the flux of particles reaching the earth's surface, as well as cases of simultaneous arrival at the observation level of groups of particles -- very small Extensive Air Showers, require simulation calculations and taking into account a much greater extent of fluctuations of the development of the showers generated by very low energy cosmic ray particles, much greater than usual for showers with energies near the "knee" and above due to the very steep cosmic ray energy spectrum. These fluctuation depend significantly on the mass number of the primary cosmic ray particle. Nuclei are sets of nucleons and it seems an obvious approximation to assume that the extensive air showers initiated in the upper atmosphere by atomic nuclei are a convolution of the showers generated by single nucleons. This is called the superposition hypothesis. In this paper, we test this superposition model. We will show, using results of a detailed simulation program CORSIKA, that the superposition assumption is not fulfilled for higher moments of the distributions of the main characteristics of extensive air showers. We will discussed some extensions of the simply superposition model that ensure consistency with the results of detailed simulations.