Atmospheric neutrinos:: LMA oscillations, Ue3 induced interference and CP-violation

We consider oscillations of the low energy (sub-GeV sample) atmospheric neutrinos in the three neutrino context. We present the semi-analytic study of the neutrino evolution and calculate characteristics of the e-like events (total number, energy spectra and zenith angle distributions) in the presence of oscillations. At low energies there are three different contributions to the number of events: the LMA contribution (from nu(e)-oscillations driven by the solar oscillation parameters), the U-e3-contribution proportional to s(13)(2), and the U-e3-induced interference of the two amplitudes driven by the solar oscillation parameters. The interference term is sensitive to the CP-violation phase. We describe in details properties of these contributions. We find that the LMA, the interference and U-e3 contributions can reach 5-6%, 2-3% and 1-2% correspondingly. An existence of the significant (> 3-5%) excess of the e-like events in the sub-GeV sample and the absence of the excess in the multi-GeV range testifies for deviation of the 2-3 mixing from maximum. We consider a possibility to measure the deviation as well as the CP-violation phase in future atmospheric neutrino studies. (C) 2004 Elsevier B.V. All rights reserved.