On absorption of the hadron component of EAS cores in a large lead calorimeter at ‘knee’-range energies

Abstract

The absorption of the core particles of extensive air showers (EAS) in the large 36 m2 lead ionization calorimeter (at the Tien-Shan mountain station) is analyzed in comparison with full Monte Carlo simulations. The EAS development in the atmosphere is simulated in the framework of CORSIKA+QGSJET code whereas the passage of hadrons and muons through the calorimeter has been simulated using the FLUKA transport code. It is shown that in EAS with energies of a few PeV the value of absorption length, Λ, of core hadron energy increases with energy much faster than that expected from simulations. This effect may be connected with the appearance of a small (a few per cent) excess of abnormal EAS cores with large ionization deposited in the lower layers of the calorimeter. It is shown that the shape of ionization curves in the lead calorimeter observed in abnormal EAS resembles that of high-energy muon groups. This effect cannot be explained by the increase of heavy nuclei in the PCR in the knee region. The hypothesis of prompt muons originated in the interaction of particles with atomic nuclei in the atmosphere also cannot explain the excess of abnormal absorption even at large values of charmed particle production cross sections.