The aim of this report of the Working Group on Hadronic Interactions and Air Shower Simulation is to give an overview of the status of the field, emphasizing open questions and a comparison of relevant results of the different experiments. It is show
n that an approximate overall understanding of extensive air showers and the corresponding hadronic interactions has been reached. The simulations provide a qualitative description of the bulk of the air shower observables. Discrepancies are however found when the correlation between measurements of the longitudinal shower profile are compared to that of the lateral particle distributions at ground. The report concludes with a list of important problems that should be addressed to make progress in understanding hadronic interactions and, hence, improve the reliability of air shower simulations.
The proton-air inelastic cross section value sigmapairin=338$pm$21({it stat})$pm$19({it syst})-28({it syst}) mb at $sqrt{s} approx $ 2 TeV has been measured by the EAS-TOP Extensive Air Shower experiment. The absorption length of cosmic ray proton pr
imaries cascades reaching the maximum development at the observation level is obtained from the flux attenuation for different zenith angles (i.e. atmospheric depths). The analysis, including the effects of the heavier primaries contribution and systematic uncertainties, is described. The experimental result is compared with different high energy interaction models and the relationships with the {it pp} ($bar pp$) total cross section measurements are discussed.
