Kneelike structure in the spectrum of the heavy component of cosmic rays observed with KASCADE-Grande

TL;DR

This paper reports the detection of a spectral steepening in heavy primary cosmic rays around 8×10^{16} eV, indicating a new feature in the cosmic ray spectrum distinct from the well-known knee.

Contribution

It presents the first observation of a heavy component knee in the cosmic ray spectrum using KASCADE-Grande data, based on independent measurements of air shower components.

Findings

Identification of a steepening in heavy primary spectrum at 8×10^{16} eV

Confirmation that the heavy component causes the new spectral feature

Analysis of charged particle and muon data on a single-event basis

Abstract

We report the observation of a steepening in the cosmic ray energy spectrum of heavy primary particles at about $8 \times 10^{16}$ eV. This structure is also seen in the all-particle energy spectrum, but is less significant. Whereas the `knee' of the cosmic ray spectrum at $3-5 \times 10^{15}$ eV was assigned to light primary masses by the KASCADE experiment, the new structure found by the KASCADE-Grande experiment is caused by heavy primaries. The result is obtained by independent measurements of the charged particle and muon components of the secondary particles of extensive air showers in the primary energy range of $10^{16}$ to $10^{18}$ eV. The data are analyzed on a single-event basis taking into account also the correlation of the two observables.