Neutrinos and muons from atmospheric charm

We evaluate the fluxes of neutrinos and muons from charmed particles produced by cosmic ray interactions with air nuclei. Using next-to-leading order perturbative QCD, we compare our results with calculations based on a PYTHIA Monte Carlo evaluation of charm production. We investigate the sensitivity of our results to the choice of parton distribution functions and the cosmic ray spectrum. Perturbative QCD yields larger lepton fluxes than the PYTHIA evaluation. The flux of muons from charm dominates the muon flux from pion and kaon decays for energies above $\sim 10^5$ GeV.