Properties of cosmic ray interactions at PeV energies

An analysis has been made of the present situation with the high energy hadron–nucleus and nucleus–nucleus interaction models. As is already known there are inconsistencies in the interpretation of experimental data on the primary mass composition, which appear when different EAS components are used for the analyses, even for the same experiment. In the absence of obvious experimental defects, there is a clear need for an improvement to the existing models; we argue that the most promising way is to introduce two effects which should be present in nucleus–nucleus collisions and have not been allowed for before. These are: a few percent energy transfer into the EAS electromagnetic component due to electron–positron pair production or electromagnetic radiation of quark-gluon plasma and a small slow-down of the cascading process in its initial stages associated with the extended lifetime of excited nuclear fragments. The latter process displaces the shower maximum deeper into the atmosphere.