A new measurement of the atmospheric proton and muon fluxes

We report on a new measurement of the momentum spectra of protons as well as of positive and negative muons as a function of atmospheric depth in the momentum ranges 0.5-40, 0.3-2 and 0.3-40 GeV/c, respectively. The measurements were carried out by the CAPRICE94 experiment from Lynn Lake, Manitoba, Canada, 8-9 August 1994. The measured muon flux values have been compared with the spectra obtained from one dimensional simulations, which were carried out to interpret the atmospheric neutrino data. We find that our data of the absolute muon flux disagree with the results from these simulations. The ratio of the muon flux derived from simulations to that measured is at largest 1.8 and varies with atmospheric depth and muon momentum. Also the measured ratio of the flux of positive and negative muons at 3.9 g/cm overburden differs significantly from the simulations. The atmospheric proton flux could be a valuable independent cross-check of the simulation results.