  The primary proton spectrum up to 100 TeV has been investigated by balloon-
and satellite-borne instruments. Above this energy range only ground-based air
shower arrays can measure the cosmic ray spectrum with a technique moderately
sensitive to nuclear composition. An array which exploits the full coverage
approach at very high altitude can achieve an energy threshold well below the
TeV region, thus allowing, in principle, the inter-calibration of the measured
proton content in the primary cosmic ray flux with the existing direct
measurements from balloons/satellites.
  The capability of the ARGO-YBJ experiment, located at the YangBaJing Cosmic
Ray Laboratory (4300 m a.s.l., Tibet, P.R. China), in selecting the surviving
primary cosmic ray protons is discussed. A procedure looking for
quasi-unaccompanied events with a very steep lateral distribution is also
presented.

Astrophysics