Observation of a knee in the p+He energy spectrum below 1 PeV by using an hybrid measurement with ARGO-YBJ and a LHAASO cherenkov telescope

Abstract

The measurement of the cosmic ray energy spectrum, in particular for individual nuclei, is an important tool to investigate acceleration and propagation mechanisms. The determination of the 'knees' in the spectra of different species is one of the main open problems in the cosmic ray physics. In fact, experimental results are still conflicting. In this paper we report a measure- ment of the mixed proton and Helium energy spectrum using the combination of the ARGO-YBJ experiment and of a wide field of view Cherenkov telescope, prototype of the future LHAASO experiment. The detectors are located at the Yangbajing Cosmic Ray Observatory (Tibet, P.R. China, 4300 m above sea level, 606 g/cm2). By means of a multi-parameter technique we se- lected a high purity proton plus Helium sample. A uniform energy resolution of about 25% throughout the whole investigated energy range (100 TeV - 3 PeV) is obtained. A knee-like fea- ture at 700±230 (stat:)±70 (sys:) TeV, with a clear steepening of the light component spectrum, is observed. This is in agreement with other two independent analysis of ARGO-YBJ data, and provides new important inputs to acceleration/propagation models for galactic cosmic rays.