Longitudinal development of gamma-ray extensive air shower in the knee and ankle energy ranges

Identifying the longitudinal profile of extensive air showers (EAS) is crucial for investigating the origin and characteristics of ultra-high-energy cosmic rays. This study simulates gamma-ray-induced EAS in the knee 1015 eV and ankle 1018 - 1020 eV energy ranges using the AIR-shower Extended Simulations (AIRES) system (Version 19.04.10) with QGSJET II 04 and EPOS LHC hadronic models at zenith angles of 0° and 25°. The shower patterns are parameterized using a Gaussian amplitude function, which reveals that the shower maximum Xmax develops logarithmically with primary energy. Gamma-ray density peaks in deeper atmospheric layers ∼580 - 864 g/cm2 for higher energies. Particularly, slanted showers 25° display wider particle distributions due to longer atmospheric path lengths, which is consistent with CORSIKA. These findings limit the harmonic interaction models for the Telescope Array and LHAASO experiments, thereby reducing systematic errors in cosmic ray composition analysis.