Exact Formula of Probability and CP Violation for Neutrino Oscillations in Matter

Within the framework of the standard three neutrino scenario, we derive an exact and simple formula of the oscillation probability $P(\nu_e \to \nu_{\mu})$ in constant matter by using a new method. From this formula, it is found that the matter effects can be separated from the pure CP violation effects. Furthermore, the oscillation probability can be written in the form, $P(\nu_e \to \nu_{\mu})=A\cos \delta+B\sin\delta+C$, in the standard parametrization without any approximation. We also demonstrate that the approximate formula in high-energy can be easily reproduced from this as an example.