The ARGO–YBJ experiment is a full–coverage air shower detector located at the Yangbajing Cosmic Ray Observatory ( Tibet , People ’ s Republic of China , 4300 m a.s.l . ) .
The high altitude , combined with the full–coverage technique , allows the detection of extensive air showers in a wide energy range and offer the possibility of measuring the cosmic ray proton plus helium spectrum down to the TeV region , where direct balloon/space–borne measurements are available .
The detector has been in stable data taking in its full configuration from November 2007 to February 2013 .
In this paper the measurement of the cosmic ray proton plus helium energy spectrum is presented in the region 3 - 300 TeV by analyzing the full collected data sample .
The resulting spectral index is \gamma = -2.64 \pm 0.01 .
These results demonstrate the possibility of performing an accurate measurement of the spectrum of light elements with a ground based air shower detector .