Cosmic ray studies around the “knee” of the primary spectrum from EAS-TOP

Abstract

The experimental information on primary cosmic rays in the energy range 1014 – 1016 eV is discussed following the present data from the EAS-TOP array (Campo Imperatore, 2000 m a.s.l., INFN National Gran Sasso Laboratories). The data on the “knee”, as observed in the electromagnetic and muon components (Eμ ≥ GeV) are presented. They are consistent both concerning the intensity and the primary energy of the break, and the slopes of the spectra below and above the steepening. From the e.m. size spectrum: the shape of the break, the dependence of its size on the atmospheric depth and the primary energy spectrum are derived. The data on the sidereal anisotropy at Ēo ≈ 2. · 1014 eV are discussed. The anisotropy is measured with good statistical accuracy: its amplitude is significantly smaller than expected from the diffusion models constructed at 109 – 1011 eV, showing that such models cannot be naively extrapolated to the 1014 eV energy range.