Measurement of the cosmic ray spectrum and chemical composition in the 10¹⁵-10¹⁸ eV energy range

Dipartimento di Fisica dell’Universitá degli Studi di Torino & INFN Via Pietro Giuria 1, 10125, Torino, Italy

^* e-mail: achavas@to.infn.it

Published online: 26 January 2018

Abstract

Cosmic ray in the 10¹⁵–10¹⁸ eV energy range can only be detected with ground based experiments, sampling Extensive Air Showers (EAS) particles. The interest in this energetic interval is related to the search of the knee of the iron component of cosmic ray and to the study of the transition between galactic and extra-galactic primaries. The energy and mass calibration of these arrays can only be performed with complete EAS simulations as no sources are available for an absolute calibration. The systematic error on the energy assignment can be estimated around 30 ± 10%. The all particle spectrum measured in this energy range is more structured than previously thought, showing some faint features: a hardening slightly above 10¹⁶ eV and a steepening below 10¹⁷ eV. The studies of the primary chemical composition are quickly evolving towards the measurements of the primary spectra of different mass groups: up to now we are able to separate (on a event by event basis) light and heavy primaries. Above the knee a steepening of the heavy primary spectrum and a hardening of the light ones have been detected.