Cosmic-ray energy spectrum from 10¹⁵ to 10¹⁸ eV

Abstract

THE problem of establishing the primary cosmic-ray energy spectrum at energies ≳ 10¹⁵ eV, a region of great astrophysical interest, depends for its solution on the relation between the size and total primary energy of extensive air showers. This is because the experimental data are directly related to extensive air shower size spectra, which must then be converted to a primary energy spectrum. The necessary conversion depends, among other things, on the physics of the hadronic part of the cascade and on the primary composition in an energy region in which such information is only available from extensive air showers themselves. The primary energy spectrum above 10¹⁵ eV is thus less well established than it is, for example, below 10¹² eV, where direct measurements have been made, both of cosmic-ray primaries and of individual hadronic interactions.