Measurement of the flux of atmospheric muons with the CAPRICE94 apparatus

A new measurement of the momentum spectra of both positive and negative muons as a function of atmospheric depth was made by the balloon-borne experiment CAPRICE94. The data were collected during ground runs in Lynn Lake on 19 and 20 July 1994 and during the balloon flight on 8 and 9 August 1994. We present results that cover the momentum intervals 0. 3--40 GeV/c for ^- and 0. 3--2 GeV/c for ^+, for atmospheric depths from 3. 3 to 1000 g/cm^2, respectively. Good agreement is found with previous measurements for high momenta, while at momenta below 1 GeV/c we find latitude dependent geomagnetic effects. These measurements are important cross-checks for the simulations carried out to calculate the atmospheric neutrino fluxes and to understand the observed atmospheric neutrino anomaly.