Time structure of individual extensive air showers

Extensive air showers detected by the GREX array have been sampled by means of highly segmented 8 m(2) bakelite RPC in the GREX/COVER_PLASTEX experime nt, Delay distributions of particles with respect to the first arriving par ticle in the EAS front at PeV energies have been analysed for individual ev ents in the core distance range of 0-100 m, It is shown that both mean arri val time and EAS front thickness in individual showers fluctuate strongly a nd cannot be a good measure of the distance from the EAS axis in a 0-100 m core distance interval. Individual distributions have been compared with integrated inclusive distr ibutions measured in the same experiment, Results indicate that the width o f the individual distribution is systematically less than that of the inclu sive distribution. It means that the bulk of particles in individual shower s arrive as a relatively compact group delayed by different time intervals from the first arriving particle. Such fluctuations of the arrival time for most of the shower particles may be the consequence of large fluctuations in the shower longitudinal development. Comparison with CORSIKA Monte Carlo simulations confirmed the difference be tween the mean width of inclusive and individual arrival time distribution. It revealed also the presence in the experiment of the excessive train of delayed particles near the shower cope. This train is obviously due to the non-relativistic low energy hadrons most abundant in the shower core region . (C) 1999 Elsevier Science B.V, All rights reserved.