Past exam of the particle physics course of the University of Oxford / 2022 / 6 / d / vii

In vacuum the electron-flavour survival probability depends only on $|U_{ei}{|}^2$ and the mass-squared differences. Complex conjugation of the lepton mixing matrix therefore leaves it unchanged:Thus a reactor disappearance measurement cannot search for the intrinsic CP violation phase in the standard three-neutrino model. Sensitivity to that phase calls for suitable appearance channels and, usually, comparison of neutrino and antineutrino beams. Matter can produce differences between propagation of neutrinos and antineutrinos; these are not by themselves intrinsic CP violation, and are small for the proposed short reactor baseline.