Abstract
This review of atmospheric muons and neutrinos emphasizes the high energy range relevant for backgrounds to high-energy neutrinos of astrophysical origin. After a brief historical introduction, the main distinguishing features of atmospheric νμ and νe are discussed, along with the implications of the muon charge ratio for the νµ / νµ ratio. Methods to account for effects of the knee in the primary cosmic-ray spectrum and the energy-dependence of hadronic interactions on the neutrino fluxes are discussed and illustrated in the context of recent results from IceCube. A simple numerical/analytic method is proposed for systematic investigation of uncertainties in neutrino fluxes arising from uncertainties in the primary cosmic-ray spectrum/composition and hadronic interactions.
Highlights
Atmospheric leptons are of current interest in two contexts, as a beam for the study of neutrino oscillations and the mass hierarchy and as the background in the search for high energy neutrinos of astrophysical origin
The emphasis of this paper is on the higher energy range, motivated by the discovery by IceCube [1, 2] of neutrinos of extraterrestrial origin at very high energy above the background of atmospheric neutrinos
Perhaps less well known is the early (1961) paper [6] by Zatsepin and Kuz’min in which the essential phenomenology of atmospheric neutrinos is derived, including the important role of kaons relative to pions as parents of neutrinos. Their papers include the production of neutrinos from decay of muons, and they describe the strong angular dependence at high energy, which is a consequence of the sec θ dependence of the ratio of decay to interaction above the critical energies of the mesons. They explain that charged kaons are more efficient producers of neutrinos than charged pions because of the higher mass of the kaon relative to the muon and the shorter lifetime of the kaon
Summary
Atmospheric leptons are of current interest in two contexts, as a beam for the study of neutrino oscillations and the mass hierarchy (energy range 100 MeV→TeV) and as the background in the search for high energy neutrinos of astrophysical origin (energy range 100 GeV→PeV). The emphasis of this paper is on the higher energy range, motivated by the discovery by IceCube [1, 2] of neutrinos of extraterrestrial origin at very high energy above the background of atmospheric neutrinos. In view of this discovery it is important to understand the atmospheric neutrino spectrum as precisely as possible, to understand the backgrounds, and in order to learn how the spectrum of the astrophysical component extends to lower energy
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