Monte Carlo simulation of the HEGRA cosmic ray detector performance

Models of the scintillator and wide-angle air Cherenkov (AIROBICC) arrays of the HEGRA experiment are described here. Their response to extensive air showers generated by cosmic rays in the 10 to 1000 TeV range has been assessed using a detailed Monte Carlo simulation of air shower development and associated Cherenkov emission. Protons, γ-rays and oxygen and iron nuclei have been considered as primary particles. For both arrays, the angular resolution as determined from the Monte Carlo simulation is compared with experimental data. Shower size Ne can be reconstructed from the scintillator signals with an error ranging from 10% (Ne = 2 × 105) to 35% (Ne = 3 × 103). The energy threshold of AIROBICC is 14 TeV for primary gammas and 27 TeV for protons and an angular resolution of 0.25° can be obtained. The measurement of the Cherenkov light at 90 m from the shower core provides an accurate determination of primary energy E0 as far as the nature of the primary particle is known. For gammas an error in the energy prediction ranging from 8% (E0 = 5 × 1014 eV) to 15% (E0 = 2 × 1013 eV) is achieved. This detector is therefore a powerful tool for γ-ray astronomy.