The Knee of the Cosmic Hydrogen and Helium Spectrum below 1 PeV Measured by ARGO-YBJ and a Cherenkov Telescope of LHAASO

Understand

The measurement of cosmic ray energy spectra, in particular for individual species, is an essential approach in finding their origin.

• Locating the "knees" of the spectra is an important part of the approach and has yet to be achieved.
• Here we report a measurement of the mixed Hydrogen and Helium spectrum using the combination of the ARGO-YBJ experiment and of a prototype Cherenkov telescope for the LHAASO experiment.
• A knee feature at 640+/-87 TeV, with a clear steepening of the spectrum, is observed.