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 cm2 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: Sh(Eh)=(2.25±0.21 ±0.34^sys) x 10^-7 (Eh/1000)^(—2.79±0.05) m^2s^-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 CORSIK.A/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 E0 = 0.5—50 TeV its best fit is given by a single power law: S(Eo) = (9.8 ± 1.1 ± 1.6^sys) x 10^-5 (Eh/1000)^(—2.80±0.06) m^2s^-1 sr^-1 GeV^-1