Shower simulation: Lessons from MOCCA

The paper describes one approach to the Monte-Carlo simulation of extensive air showers of energy in the range 10(12) to 10(21) eV, using thin sampling for particles of energy much below the energy of the primary particle. Experience of this approach using the MOCCA program is outlined. Also, it is argued that only a few features of hadronic interactions are important in determining shower properties, and that the far plateau region of particle production is of little importance, and hence a simplified hadron interaction algorithm, as employed in MOCCA, is useful. Methods of demonstrating the contribution of different features of the interactions to observable aspects of showers are illustrated. The importance of secondary spectra from pion-air collisions in influencing the depth of maximum is highlighted.