Figure 1: Schematic diagramm of ν oscillations in a simplified two-neutrino scheme: The muon neutrino νμ is a superposition of the mass eigenstates νi when produced e.g. in a particle accelerator target or in the earth´s atmosphere. After a travelling distance L or travel time t, the phases between the mass eigenstates changed, i.e. the composition changed, so that it corresponds to the mixture called νe. The oscillation probability P for such a change of the neutrino "flavor" eigenstate (the eigenstate of the weak interaction) can be described as a function of the neutrino energy Eν, the difference of the squared masses Δm212=|m12-m22| and the mixing angleΘ. Whereas the mass difference determines the spatial evolution, the amplitude of the oscillation is given by the mixing angle.