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

Abstract

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 ${\ensuremath{\mu}}^{+}/{\ensuremath{\mu}}^{\ensuremath{-}}$ is presented as a function of atmospheric depth in the momentum interval 0.3--0.9 $\mathrm{GeV}/c.$ The differential ${\ensuremath{\mu}}^{\ensuremath{-}}$ momentum spectra are presented between 0.3 and $\ensuremath{\sim}50$ $\mathrm{GeV}/c$ at atmospheric depths between 13 and 960 ${\mathrm{g}/\mathrm{c}\mathrm{m}}^{2}.$ 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 ${\ensuremath{\mu}}^{\ensuremath{-}}$ fluxes are smaller than the predictions by as much as 70% at shallow atmospheric depths, by $\ensuremath{\sim}20%$ 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.