CP violation and matter effect in long-baseline neutrino oscillation in the four-neutrino model
Abstract
We investigate the CP violation effect and the matter effect in long-baseline neutrino oscillations in the four-neutrino model with mass scheme of the two pairs of close masses separated by a gap of the order of 1 eV, by using the results of the combined analyses of the neutrino oscillation solutions to the solar and atmospheric neutrino problems with the recent SNO solar neutrino data. The behavior of the pure CP violation effect is quite different from the one in the three-neutrino case due to the existence of the LSND neutrino mass scale of \Delta m^2_{LSND} = (0.2-1) eV^2. The pure CP violation part of the oscillation probability difference between the CP-conjugate channels is sizable and is as large as 5-15% in the neutrino energy range of E = a few - 20 GeV for \nu_\mu \to \nu_\tau oscillation for the distance L = 250 and 730 km, and the matter effect is negligibly small. On the contrary, for \nu_\mu \to \nu_e oscillation, the pure CP violation effect is at most 1-2% in E = 3-10 GeV for L = 250 km and the matter effect attains as large as 1/4 to 1/2 of the pure CP violation effect.Keywords
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