Energy spectra, altitude profiles, and charge ratios of atmospheric muons

We present a new measurement of air shower muons made during atmospheric ascent of the High Energy Antimatter Telescope balloon experiment. The muon charge ratio μ⁺/μ^- is presented as a function of atmospheric depth in the momentum interval 0.3-0.9 GeV/c. The differential μ^- momentum spectra are presented between 0.3 and ∼50 GeV/c at atmospheric depths between 13 and 960 g/cm². We compare our measurements with other recent data and with Monte Carlo calculations of the same type as those used in predicting atmospheric neutrino fluxes. We find that our measured μ^- fluxes are smaller than the predictions by as much as 70% at shallow atmospheric depths, by ∼20% at the depth of shower maximum, and are in good agreement with the predictions at greater depths. We explore the consequences of this on the question of atmospheric neutrino production.