Production of muons and neutrinos in cosmic ray interactions with the atmosphere has been investigated with Monte Carlo models for hadronic interactions. The resulting conventional muon and neutrino fluxes (from π and K decays) agree well with earlier calculations, whereas our prompt fluxes from charm decays are significantly lower than earlier estimates. Charm production is mainly considered as a well defined perturbative QCD process, but we also investigate a hypothetical nonperturbative intrinsic charm component in the proton. The lower charm rate implies better prospects for detecting very high energy neutrinos from cosmic sources. IntroductionThe flux of muons and neutrinos at the earth has an important contribution from decays of particles produced through the interaction of cosmic rays in the atmosphere (for a recent introduction see [1]). This has an interest in its own right, since it reflects primary interactions at energies that can by far exceed the highest available accelerator energies. It is also a background in studies of neutrinos from cosmic sources as attempted in large neutrino telescopes, such as Amanda [2], Baikal [3], Dumand [4] and Nestor [5].Here we present a detailed study of muon and neutrino production in cosmic ray interactions with nuclei in the atmosphere using Monte Carlo simulations [6].At GeV energies the atmospheric muon and neutrino fluxes are dominated by 'conventional' sources, i.e. decays of relatively long-lived particles such as π and K mesons. This is well understood from earlier studies [7,8,9], with which our investigations agree. With increasing energy, the probability increases that such particles interact in the atmosphere before decaying. This implies that even a small fraction of short-lived particles can give the dominant contribution to high energy muon and neutrino fluxes. These 'prompt' muons and neutrinos arise through semi-leptonic decays of hadrons containing heavy quarks, most notably charm.Available data in the multi-TeV energy range, obtained with surface and underground detectors (see e.g. refs. [10][11][12][13]), are still too discrepant to draw definitive conclusions on the flux of 1 thunman@tsl.uu.se 2 ingelman@tsl.uu.se, also at DESY, Hamburg.

The flux of neutrinos originating from cosmic ray interactions with matter in the Sun has been calculated based on Monte Carlo models for high energy particle interactions. The resulting flux at the Earth (within the Sun's solid angle) is higher than the corresponding one from cosmic ray interactions with the Earth atmosphere. The smallness of the absolute rate, however, precludes it as a practical 'standard candle' for neutrino telescopes and limits neutrino oscillation searches. On the other hand, it facilitates dark matter searches based on neutrinos from neutralino annihilation in the Sun.

Production of muons and neutrinos in cosmic ray interactions with the atmosphere has been investigated with a cascade simulation program based on Lund Monte Carlo programs. The resulting`conventional' muon and neutrino uxes (from ; K decays) agree well with earlier calculations, whereas the improved charm particle treatment used in this study gives signi cantly lower`prompt' uxes compared to earlier estimates. This implies better prospects for detecting very high energy neutrinos from cosmic sources.

The prospects to test the hypothesis of intrinsic charm quarks in the proton are investigated. We consider how this component can be directly or indirectly probed in deep inelastic scattering at HERA and in fixed target experiments and find that an overlooked signal might be present in existing NMC data. Applying the intrinsic charm model to hadron collisions we compare the resulting charm production cross-sections with those based on standard perturbative QCD and available data. Extrapolating to higher energies we obtain predictions for charm production at the Tevatron and LHC.

We have updated our previous investigation of the production of muons and neutrinos in cosmic ray interactions with the atmosphere, taking account of recent results from the $ep$ collider HERA in our QCD-based model for hadronic interactions. Qualitatively, our previous results remain unmodified: our predictions for the conventional muon and neutrino fluxes agree with earlier calculations, whereas the charm particle treatment we use gives significantly lower prompt fluxes compared to earlier estimates. This implies better prospects for detecting very high energy neutrinos from cosmic sources.Comment: Talk presented by P. Gondolo at TAUP95, Toledo, Sept. 1995. 3 pages, 2 Postscript figures, uses epsf.sty and espcrc2.st