Detection of a change of slope in the spectrum of heavy mass cosmic rays primaries by the Kascade-Grande experiment

Abstract

KASCADE-Grande is an extensive air shower experiment devoted to the study of cosmic rays in the '10 POT. 16' ÷ '10 POT. 18' eV energy range. The array comprises various detectors allowing independent measurements of the number of muons (Nμ) and charged particles (Nch) of extensive air showers (EAS). These two observables are then used to study the primary energy spectrum, separating the events into two samples on the basis of the shower size ratio, corrected for attenuation in the atmosphere, lnNμ/ lnNch. The two samples represent the light and heavy mass groups of the primaries. In the studied energy range, only the spectrum of heavy primaries shows a significant change of slope. The energy (estimated using the QGSJET II hadronic interaction model) of this feature is in agreement with the expectations of a rigidity-dependent knee feature.