Air shower array at the university of Puebla for the study of cosmic rays

Abstract

We describe the design and performance of an extensive air shower detector array built in the Campus of the University of Puebla (located at 19$^\circ$N, 90$^\circ$W, 800 g/cm$^{2}$) to measure the energy and arrival direction of primary cosmic rays with energies around 10$^{15}$~eV, known as the knee of the cosmic ray spectrum. The array consists of 18 liquid scintillator detectors (12 in the first stage), and 3 water Cherenkov detectors (one of 10 m$^{2}$ cross section and two smaller ones of 1.86 m$^{2}$ cross section), distributed in a square grid with a detector spacing of 20 m over an area of 4000 m$^{2}$. In this paper, we discuss the calibration and stability of the array and report on preliminary measurements of the arrival directions and energies of cosmic ray showers detected with the first stage of the array consisting of 12 liquid scintillator and 3 water Cherenkov detectors. Our results show that the array is efficient in detecting primary cosmic rays with energies in the range of 10$^{14}$ to 10$^{16}$~eV, with an angular resolution lower than 5.5$^\circ$ for zenithal angles in the range of 20$^\circ$ to 60$^\circ$. We also point out that the capability of water Cherenkov detectors to separate electromagnetic from muon components of extensive air showers. Finally we remark that this facility is also used to train students interested in the field of cosmic rays.