Behaviour of the high-energy neutrino flux in the earth’s atmosphere

The processing of the IceCube experiment data, obtained during 988 days (2010-2013), revealed 37 high-energy neutrino-induced events with deposited energies 30 TeV - 2 PeV. The hypothesis of an astrophysical origin of these neutrinos is confirmed at the statistical confidence level of 5.7 standard deviations. To identify reliably the neutrino events, a thorough calculation of the atmospheric neutrino background is required. In this work we calculate the atmospheric neutrino spectra in the energy range 100 GeV - 10 PeV with usage of several hadronic models and a few parametrizations of the cosmic ray spectra, supported by experimental data, which take into account the knee. It is shown that rare decays of short-lived neutral каоns K0_s contribute more than a third of the total electron neutrino flux at the energies above 100 ТeV. The account for kaons production in pion-nucleus collisions increases the electron neutrino flux by 5-7 % in the energy range 10^2 -10^4 GeV. Calculated neutrino spectra agree on the whole with the measurement data. The neutrino flavor ratio, extracted from the IceCube data, possibly indicates that the conventional atmospheric electron neutrino flux obtained in the IceCube experiment contains an admixture of the astrophysical neutrinos in the range 20 - 50 TeV.