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 $\mathrm{GeV}/c$ for ${\mathrm{\mu }\mathrm{}}^{\mathrm{-}}$ and 0.3–2 $\mathrm{GeV}/c$ for ${\mathrm{\mu }\mathrm{}}^{+},$ for atmospheric depths from 3.3 to 1000 ${\mathrm{g}/\mathrm{c}\mathrm{m}}^2,$ respectively. Good agreement is found with previous measurements for high momenta, while at momenta below 1 $\mathrm{GeV}/c$ 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.

• Received 2 February 2000

DOI:https://doi.org/10.1103/PhysRevD.62.032007