A simulation study on the performance of the ALPAQUITA experiment

The ALPACA experiment is a new air shower experiment mainly aiming to explore the southern sky in the VHE gamma-ray regime beyond 100 TeV. As the prototype experiment, ALPAQUITA will start in late 2021. It consists of a surface air shower array (18, 450 m²) and an underground muon detector array (900 m²). In this study, the performance of ALPAQUITA including the sensitivity to gamma-ray point sources is investigated using a Monte Carlo simulation to quantitatively evaluate the possibility of detection of gamma-ray sources in the prototype phase. Corsika 7.6400 and Geant4 v10.04.p02 are used to simulate air shower development in the atmosphere and detector response, respectively. The output data are then processed and analyzed in the same way as the experiment. As a result, the study finds that the air shower array has an energy resolution of ±21% and the angular resolution of ≃ 0.2^◦ for gamma rays with an energy of 100 TeV. The detection area of the air shower array for gamma rays reaches ≃ 12, 600 m² above ≃ 30 TeV. The muon detector rejects ≃ 99.9% of background cosmic rays and maintains ≃ 80% of signal gamma rays. This high discrimination power will enable the detection of five southern known gamma-ray sources beyond 30 TeV and the extension of the energy spectrum of one out of the five, HESS J1702-420A, up to ≃ 300 TeV during one calendar year observation. This study concludes that ALPAQUITA will provide data enough to discuss a hot topic of VHE gamma-ray astronomy before passing the baton to ALPACA.