A simulation study on few parameters of Cherenkov photons in extensive air showers of different primaries incident at various zenith angles over a high altitude observation level

We have studied the distribution patterns of lateral density, arrival time and angular position of Cherenkov photons generated in Extensive Air Showers (EASs) initiated by $gamma$-ray, proton and iron primaries incident with various energies and at various zenith angles. This study is the extension of our earlier work cite{Hazarika} to cover a wide energy range of ground based $gamma$-ray astronomy with a wide range of zenith angles ($le 40^circ$) of primary particles, as well as the extension to study the angular distribution patterns of Cherenkov photons in EASs. This type of study is important for distinguishing the $gamma$-ray initiated showers from the hadronic showers in the ground based $gamma$-ray astronomy, where Atmospheric Cherenkov Technique (ACT) is being used. Importantly, such study gives an insight on the nature of $gamma$-ray and hadronic showers in general. In this work, the CORSIKA 6.990 simulation code is used for generation of EASs. Similarly to the case of Ref.cite{Hazarika}, this study also revealed that, the lateral density and arrival time distributions of Cherenkov photons vary almost in accordance with the functions: $rho_{ch}(r) = rho_{0};e^{-beta r}$ and $t_{ch}(r) = t_{0}e^{Gamma/r^{lambda}}$ respectively by taking different values of the parameters of functions for the type, energy and zenith angle of the primary particle. The distribution of Cherenkov photons angular positions with respect to shower axis shows distinctive features depending on the primary type, its energy and the zenith angle.