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

Abstract

The flux of cosmic ray hadrons at the atmospheric depth of 820 g cm −2 has been measured by means of the EAS-TOP 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 )×10 −7 E h 1000 (−2.79±0.05) m −2 s −1 sr −1 GeV −1 overthe 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)=(9.8±1.1±1.6 sys )×10 −5 E 0 1000 (−2.80±0.06) m −2 s −1 sr −1 GeV −1 The validity of the CORSIKA/QGSJET code for such application has been checked using the EAS-TOP and KASCADE experimental data by reproducing the ratio of the measured hadron fluxes at the two experimental depths (820 and 1030 g cm −2 respectively) at better than 10% in the considered energy range.