Measurement of the cosmic ray hadron spectrum up to 30 TeV at mountain altitude: the primary proton spectrum

The flux of cosmic ray hadrons at the atmospheric depth of 820 g cm(-2) has been measured by means of the EASTOP hadron calorimeter (Campo Imperatore, National Gran Sasso Laboratories, 2005 m a.s.l.). The hadron spectrum is well described by a single power law: S-h(E-h) = (2.25 +/- 0.21 +/- 0.34(sys)) x 10(-7) [GRAPHICS] m(-2)s(-1)sr(-1)GeV(-1) over the energy range 30 GeV-30 TeV. The procedure and the accuracy of the measurement are discussed. The primary proton spectrum is derived from the data by using the CORSIKA/QGSJET code to compute the local hadron flux as a function of the primary proton spectrum and to calculate and subtract the heavy nuclei contribution (basing on direct measurements). Over a wide energy range E-0 = 0.5-50 TeV its best fit is given by a single power law: S(E-0) = (9.81 +/- 1.1 +/- 1.6(sys)) x 10(-5) [GRAPHICS] m(-2)s(-1)sr(-1)GeV(-1).