Vacuum electron-flavour survival probability ($P_{ee}=1-4{\sum }_{i<j}|U_{ei}{|}^2|U_{ej}{|}^2{\sin }^2(\Delta m_{ij}^{2}L/(4E))$)

For coherent relativistic vacuum propagation and a unitary lepton mixing matrix, square ${\sum }_i|U_{ei}{|}^2\exp [-i{m}_i^{2}L/(2E)]$ to obtain this probability. Only moduli of the mixing entries occur, so the ordinary three-state electron survival signal is independent of the intrinsic CP phase. Replacing two close fast phases by one is useful at short baselines but may fail over many periods.