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Low energy ground-based cosmic ray air shower experiments generally have energy threshold in the range of a few tens to a few hundreds of TeV. The shower observables are measured indirectly with an array of detectors. The atmospheric absorption of low energy secondaries limits their detection frequencies at the Earth's surface. However, due to selection effects, a tiny fraction of low energy showers, which are produced in the lower atmosphere can reach the observational level. But, due to less information of shower observables, the reconstruction of these showers are arduous. Hence, it is believed that direct measurements by experiments aboard on satellites and balloon flights are more reliable at low energies. Despite having very small efficiency (∼ 0.1%) at low energies, the large acceptance (∼ 5m2sr) of GRAPES-3 experiment allows observing primary cosmic rays down below to ∼ 1TeV and opens up the possibility to measure primary energy spectrum spanning from a few TeV to beyond cosmic ray knee (up to 1016eV), covering five orders of magnitude. The GRAPES-3 energy threshold for primary protons through Monte Carlo simulations are calculated, which gives reasonably good agreement with data. Furthermore, the total efficiencies and acceptance are also calculated for protons primaries. The ability of GRAPES-3 experiment to cover such a broader energy range may provide a unique handle to bridge the energy spectrum between direct measurements at low energies and indirect measurements at ultra-high energies. [ABSTRACT FROM AUTHOR]

The high density extensive air shower array along with large area (560 m2) muon telescope of GRAPES-3 at Ooty is used to make precise measurements of cosmic ray properties by using the secondaries produced through cascades in the Earth's atmosphere. The observed particle density at detector level is affected by atmospheric effects primarily due to variations in the pressure and temperature. Here, an attempt is made to simulate these phenomena that can provide a deeper understanding of these effects. In this study, the pressure dependence of the observed particle densities at GRAPES-3 is simulated by varying the atmospheric profiles available in CORSIKA for proton showers in the energy range of 1013–1016 eV. A comparative study of various combinations of hadronic interaction generators available in CORSIKA has been used to investigate the consistency of the results obtained and their broad implications have been intensely discussed. [ABSTRACT FROM AUTHOR]