Momentum spectra of atmospheric pions, muons, electrons and positrons at balloon altitudes

Abstract

Momentum spectra of pions, muons, electrons and secondary positrons have been measured at an atmospheric depth of with the same instrument. Data was collected by the Matter Antimatter Space Spectrometer of the New Mexico State University in a balloon flight in September 1991 at the rigidity cut-off of in Fort Sumner, New Mexico. The first measurement of the positive muon spectrum in the range to is reported in this paper. The spectral index above of the negative muon momentum spectrum of this measurement is in agreement with analytical cascade calculations which assume a primary proton kinetic energy spectrum with a slope of in the corresponding kinetic energy range. In the momentum interval 300 - , both negative and positive muon fluxes turn out to be larger than calculated fluxes by a factor of about 1.4. The measurement of the secondary electron and positron energy spectra allows a reliable subtraction of the atmospheric background from the primary electron and positron fluxes which are affected by large uncertainties in most of the experiments. The energy spectra of the secondary particles reported here have the same systematic errors implying a higher relative accuracy with respect to those measurements made in different flights.