Method for measuring the PCR proton spectrum in the energy range of > 1016 eV

Abstract

Criteria for selecting proton events among the total sequence of events from primary nuclei of cosmic rays with zenith angles θ 10 PeV; at lower energies, the average mass composition is almost unchanged. The method used in (3, 4) is based on the correlation of the Cherenkov light (CL) pulse halfwidth at a long distance from the shower axis with the shower maximum position. It is well known that the CL transverse distribution function (TDF) is also sensitive to the primary nucleus mass. However, CL detectors of ground-based installations collect light from only a small fraction of the shower area; therefore, detailed reconstruction of the CL TDF is complicated. In the SPHERE-2 experiment, it is intended to use the shape of CL TDF to determine the PCR composition, since detectors of this installation can survey about half the shower area. The operating principle of this telescope is based on the idea to measure CL produced by extended atmospheric showers (EAS) and reflected from the snow surface (7). The optical scheme of the SPHERE-2 installation represents a Schmidt camera with a mirror 1.5 m in diameter and a mosaic of 109 photomultipliers in the mirror focal surface. Thus, this system allows measurements of the quantity proportional to the total CL amount within the field of view of each detector of the mosaic. In this paper, the criteria allowing separation of a certain known proton fraction from the total number of PCR nuclei are studied using the Monte Carlo method. The Lake Baikal level (H0 = 455 m above sea level) and the detector spatial resolution δr =8 0m corresponding to the SPHERE-2 installation position at a height of 1 km over the snow surface of Lake Baikal are considered. In this case, the diameter