Atmospheric lepton fluxes at ultrahigh energies

Abstract

In order to estimate the possibility to observe exotic physics in a neutrino telescope, it is essential to first understand the flux of atmospheric neutrinos, muons and dimuons. We study the production of these leptons by high-energy cosmic rays. We identify three main sources of muons of energy E ⩾ 106 GeV: the weak decay of charm and bottom mesons and the electromagnetic decay of unflavored mesons. Contrary to the standard assumption, we find that η mesons, not the prompt decay of charm hadrons, are the dominant source of atmospheric muons at these energies. We show that, as a consequence, the ratio between the neutrino and muon fluxes is significantly reduced. For dimuons, which may be a background for long-lived staus produced near a neutrino telescope, we find that pairs of E ≈ 107 GeV forming an angle above 10−6 rad are produced through D (80%) or B (10%) meson decay and through Drell-Yan proceses (10%). The frequency of all these processes has been evaluated using the jet code PYTHIA.