Cosmic rays of superhigh and ultrahigh energies

Abstract

We present a review and analysis of the experimental data on cosmic rays with energies above 1014-1015 eV and up to 1020 eV. At the beginning a brief survey of the direct experimental data on the cosmic-ray energy spectrum and mass composition is given. We then consider the choice of the hadron interaction model at energies above 1015 eV that is essential for the interpretation of the experimental data on extensive air showers (EAS). Much attention is given to the well known knee in the primary energy spectrum at approximately 3*1015 eV and also to an analysis of this phenomenon in the framework of the recently developed Hall diffusion model. In doing so we use as yet scarce data on cosmic-ray anisotropy and mass composition at superhigh energies 1014-1017 eV. A considerable part of our review is concerned with cosmic rays of ultrahigh energies 1017-1020 eV. Using the galactic origin model for cosmic rays with energies 1014-1020 eV the possibility of explaining all the relevant data at energies above 3*1018-1019 eV is discussed: evidence of the 'ankle' in the primary energy spectrum, the upper bound of cosmic-ray anisotropy, and evidence for the increasing proton abundance. The prospects for future cosmic-ray investigations at superhigh energies are outlined and the great importance of development in the neutron and proton astronomy for energies above 1018-1019 eV is pointed out.