Validity of the superposition model for extensive air showers

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Abstract
The VENUS model of relativistic nucleus-nucleus collisions is used to study interactions of various nuclei with 14N in view of their influence on the development of extensive air showers initiated by cosmic ray nuclei in the atmosphere. As is well known, only some of the projectile nucleons take part in the interaction (participants) whereas the others (spectators) do not lose an appreciable amount of energy. Our main result is that the nucleus-nucleus collision, at the high energies of interest, can be described to a good approximation by the superposition of Np nucleon-nucleus collisions where Np is the number of participant projectile nucleons. Therefore the superposition model frequently employed in the calculation of air shower development in the atmosphere should represent a rather good approximation. This is in disagreement with some statements in the literature but is corroborated by simulation calculations of extensive air showers employing the VENUS program. Possible reasons for this discrepancy are discussed.