The energy spectrum of cosmic Hydrogen and Helium nuclei has been measured below the so-called
“knee” by using a hybrid experiment with a wide field-of-view Cherenkov telescope and the Resistive Plate Chamber
(RPC) array of the ARGO-YBJ experiment at 4300 m above sea level. The Hydrogen and Helium nuclei have been
well separated from other cosmic ray components by using a multi-parameter technique. A highly uniform energy
resolution of about 25% is achieved throughout the whole energy range (100–700 TeV). The observed energy spectrum
is compatible with a single power law with index
γ
=−2.63±0.0