ABSTRACT
In recent years the study of atmospheric neutrinos has become one of the most important fields in neutrino physics. Atmospheric neutrinos are produced in meson and muon decays, created by interactions of cosmic rays within the atmosphere. The study of these neutrinos revealed evidence for neutrino oscillations. With energies in the GeV range and baselines from about 10 km to as long as the Earth diameter (L ≈ 104 km) mass differences in the order of m2 10−4 eV2 or equivalent values in the L/E ratio from 10105 km GeV−1 are probed. Most measurements are based on relative quantities because absolute neutrino flux calculations are still affected by large uncertainties. The obtained results depend basically on four factors: the primary cosmic-ray flux and its modulations, the production cross sections of secondaries in atmospheric interactions, the neutrino interaction cross section in the detector and the detector acceptance and efficiency. More quantitatively the observed number of events is given by
dNl (θ, pl) dθ d pl
= tobs ∑ ±
∫ Nt
dφ±νl (Eν, θ) dθ dEν
dσ±(Eν, pl) d pl
F(q2) dEν (9.1)
where l stands for e± or µ±, pl the lepton momentum, Eν the neutrino energy, θ the zenith angle, tobs the observation time, Nt the number of target particles, φ±νl (Eν, θ) the neutrino flux and σ(Eν, pl) the cross section. F(q
2) takes into account the nuclear effects such as the Fermi momenta of target nucleons, Pauli blocking of recoil nucleons etc. The summation (±) is done for νl and ν¯l , since current observations do not distinguish the lepton charge. For further literature see [Sok89, Ber90b, Gai90,Lon92, 94, Gri01, Jun01, Kaj01,Lea01, Lip01, Gai02]. We want to discuss the first two steps now in a little more detail.
