CERENKOV PHOTON DENSITY-FLUCTUATIONS IN EXTENSIVE AIR SHOWERS

The details of Cerenkov light produced by a gamma-ray or a cosmic ray incident at the top of the atmosphere is best studied through systemat ic simulations of the extensive air showers. Recently such studies hav e become all the more important in view of the various techniques resu lting from such studies, to distinguish gamma-ray initiated showers fr om those generated by much more abundant hadronic component of cosmic rays. We have carried out here such systematic simulation studies usin g CORSIKA package in order to understand the Cerenkov photon density f luctuations for 5 different energies at various core distances both fo r gamma-ray and proton primaries incident vertically at the top of the atmosphere. Such a systematic comparison of shower to shower density fluctuations for gamma-ray and proton primaries is carried out for the first time here. It is found that the density fluctuations are signif icantly non-Poissonian. Such fluctuations are much more pronounced in the proton primaries than gamma-ray primaries at all energies. The pro cesses that contribute significantly to the observed fluctuations have been identified. It has been found that a significant contribution to fluctuations comes from photons emitted after the shower maximum. The electron number fluctuations and correlated emission of Cerenkov phot ons are mainly responsible for the observed fluctuations. (C) 1998 Els evier Science B.V.