Time structure of secondary particles in EAS induced by vertical gamma during thunderstorms

The temporal distribution of secondary particles in extensive air shower (EAS) is important to reconstruct the primary information of cosmic ray, such as the direction and energy. Due to acceleration/deceleration and deflection by the strong electric field in thundercloud, temporal structure of EAS disc will be changed. To study the effects of atmospheric electric field (AEF) on the time structure of EAS particles (secondary electrons, positrons and photons) produced by vertical primary gamma at LHAASO observatory level, Monte Carlo simulations are performed with CORSIKA. During thunderstorms, the temporal distributions are changed, and the variations are strongly dependent on the strength and polarity of AEF, and the types of secondary particles. In negative fields (i.e., accelerating negative charges downwards), for secondary electrons, the average arrival time are delayed and the time width are broadened. While opposite temporal variations occur in positive fields. For positrons, the patterns of temporal changes are opposite to electrons. The temporal variation amplitude increases with the field strength for both electrons and positrons. In this work, the energy dependence of the primary gammas is also discussed. These simulation results provide helpful information to further study the AEF effects on secondary particles, and enhance our understanding of the observed phenomena in ground-based experiments.