Speaker
Description
The ALPACA experiment is a new project in Bolivia designed to observe cosmic rays and gamma rays in the TeV–PeV energy range. It consists of a large air-shower array (83,000 m²) and a water-Cherenkov-type muon detector (3,600 m²) and aims to survey PeVatron candidates in the southern sky, including the Galactic Center. The surface detectors of the prototype array, ALPAQUITA, has been fully operational at the Chacaltaya plateau (4,740 m a.s.l.) in Bolivia since April 2023. It comprises 97 scintillation detectors, each with an area of 1 m², deployed with 15 m spacing.
In this research, we conducted a characterization of the scintillators used in the ALPACA and ALPAQUITA surface arrays. As a result, we obtained expressions for charge amount, signal delay, and time transit spread (t.t.s.) as functions of the distance from the center of the scintillator box. Additionally, we performed a Monte Carlo simulation using CORSIKA to generate 10⁹ cosmic ray events with energies ranging from 280 MeV to 10 PeV and reproduced the detector response using Geant4. The functions obtained from the scintillator characterization were incorporated into the detector response modeled in Geant4. As a result, the counting rates were found to be 52,000 per second for any1, 1,400 per second for any2, 530 per second for any3, and 290 per second for any4.
Furthermore, we compared the Monte Carlo data with the experimental data from ALPAQUITA for the Σρ distribution, which serves as an energy indicator of primary particles detected by the apparatus, the zenith angle distribution of the arrival direction, and the even-odd opening angle distribution, which serves as an indicator of angular resolution. In all cases, good agreement was observed.
| Collaboration(s) | ALPACA |
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