Measurement of the proton-air inelastic cross section with ARGO-YBJ

ARGO-YBJ, located in the Cosmic Ray Observatory of Yangbajing (Tibet, P.R.China) at 4300 m a.s.l., is a full-coverage Extensive Air Shower array consisting of a layer of Resistive Plate Chambers (RPC) of about 6000 m2. One of the main aims of the experiment is the cosmic ray physics in the 1012 - 1016 eV primary energy range, where the transition from direct to indirect measurements occurs. In this work the measurement of the interaction cross section between primary protons and air nuclei is reported. The analysis is based on the different flux attenuation for different atmospheric depths (i.e. zenith angles), by exploiting the detector capabilities in selecting the shower development stage by means of the size, hit density and both time and lateral profile measurements. The systematic errors introduced by fluctuations in shower development and heavier primaries have been taken into account. The results give useful insights on the p-air interactions at energies where models start to give significantly different expectations and allow to infer the p-p total cross section in an energy region (sqrt(s) = 50 GeV - 1 TeV) still scarcely explored. (authors)