Extensive air showers and the physics of high energy interactions

Extensive air showers are still the only source of information on primary cosmic-rays and their interactions at energies above PeV. However, this information is hidden inside the multiplicative character of the cascading process. Inspite of the great experimental and theoretical efforts the results of different studies are often ambiguous and even conflicting. These controversies can partly be referred to imperfections of our models of high energy particle interactions. rst part of the paper is concerned with this problem. The author thinks that the present models should be corrected to give slightly deeper penetration of the cascade into the atmosphere. In this respect the modification suggested by the QGSJET-II model seems to be the step in the right direction. The Sibyll 2.1 model provides a similar penetrating properties. However, this modification is not enough and a small additional transfer of the energy from EAS hadrons to the electromagnetic component is needed too. As a possible candidate for such a process the inelastic charge exchange of pions is discussed. second part of the paper the author discusses the need to account for the interaction of EAS with the stuff of detectors, their environment and the ground in the light of the ‘neutron thunder’ phenomenon, discovered recently.