Medium effects for terrestrial and atmospheric neutrino oscillations

Matter effects in neutrino propagation translate into effective parameters for the oscillation and fake CP- and CPT odd quantities, even in a scenario, such as Delta (12) = 0, where no genuine CP violation is present. This fact seems to impose severe restrictions on the determination of intrinsic parameters of the system from long-baseline experiments. We show, however, that the resonance in the effective mixing <(<theta>)over tilde>(13) can be observed for a certain range of baselines. This provides a way to measure the vacuum mixing angle theta (13) and the sign of Deltam(23)(2) from atmospheric neutrinos, using a detector with energy resolution and charge discrimination. (C) 2001 Elsevier Science B.V. All rights reserved.