Measuring the depth of shower maximum of extensive air showers using Cherenkov light

Abstract A method is proposed to reconstruct the depth at which showers reach the maximum number of charged particles (X max charged ) using atmospheric Cherenkov telescopes. The dependence of the Cherenkov signal with telescope distance from shower core is explored and a region in which the measurement is possible is determined (150 to 200 m). A parametrization is presented to reconstruct X max charged . The resolution of the method is studied as a function of energy, for different primary particle types and for telescope fields of view ranging from 3.5∘to 10∘. Good resolution ( ∼ 25 g/cm2) is achieved for most of the cases of primary particle type (gamma ray, proton and iron nuclei) and energy (10 TeV  40 g/cm2) is seen for energies below 30 TeV. The results presented here contribute to the understanding of the development of gamma-ray showers and suggest another possibility of using atmospheric Cherenkov telescopes to study cosmic rays in the TeV-PeV energy range.