Lateral density and arrival time distributions of Cherenkov photons in   extensive air showers: a simulation study
  We have investigated some features of the density and arrival time distributions of Cherenkov photons in extensive air showers using the CORSIKA simulation package. The main thrust of this study is to see the effect of hadronic interaction models on the production pattern of Cherenkov photons with respect to distance from the shower core. Such studies are very important in ground based $\gamma$-ray astronomy for an effective rejection of huge cosmic ray background, where the atmospheric Cherenkov technique is being used extensively within the energy range of some hundred GeV to few TeV. We have found that for all primary particles, the density distribution patterns of Cherenkov photons follow the negative exponential function with different coefficients and slopes depending on the type of primary particle, its energy and the type of interaction model combinations. Whereas the arrival time distribution patterns of Cherenkov photons follow the function of the form $t (r) = t_{0}e^{\Gamma/r^{\lambda}}$, with different values of the function parameters. There is no significant effect of hadronic interaction model combinations on the density and arrival time distributions for the $\gamma$-ray primaries. However, for the hadronic showers, the effects of the model combinations are significant under different conditions. 
P. Hazarika, U. D. Goswami, V. R. Chitnis, B. S. Acharya, G. S. Das,   B. B. Singh, R.J. Britto
astro-ph.IM astro-ph.HE hep-ex