Nuclei composition discrimination study based on Cherenkov image of air shower

Purpose In ground-based cosmic ray experiments,the Cherenkov image detected by imaging air Cherenkov telescopes contains crucial information about the longitudinal development of Extensive Air Showers,which can be used for composition discrimination between different nuclei.Methods Proton and iron showers were simulated to study the composition discrimination in the energy range from~100TeV to~10PeV with a zenith angle of 45°.A new variable,namelyθ_(x)^(max),was introduced from the longitudinal development of Cherenkov photons,which represents the posi tion at which the angular ditribution of Cherenkov photons detected by telescope reached maximum.Results Comparing to the shower maximum of Cherenkov photons(X_(Cer)^(max)),it was found that below|PeV,θ_(x)^(max)has better composition discrimination ability compared to X_(Cer)^(max)xar,while they have similar composition discrimination ability above PeV.Conclusions For nuclei composition identification,omax performed better than Xax,especially in low energies(below the PeV range).This is due to thatθ_(x)^(max)is suffering less statistical fuctuations compared to XX_(Cer)^(max)Meanwhile,θ_(x)^(max)is less afected by the statistics of Cherenkov photons compared to X_(Cer)^(max)