Correlated, Precision Measurements of θ₂₃ and δ using only the Electron Neutrino Appearance Experiments

Precision measurement of the leptonic CP violating phase $\delta$ will suffer from the, then surviving, large uncertainty of sin^2 \theta_{23} of 10-20% in the experimentally interesting region near maximal mixing of \theta_{23}. We advocate a new method for determination of both \theta_{23} and $\delta$ at the same time using only the \nu_e and \bar{\nu}_e appearance channels, and show that sin^2 \theta_{23} can be determined automatically with much higher accuracy, approximately a factor of six, than \sin \delta. In this method, we identify a new degeneracy for the simultaneous determination of \theta_{23} and \delta, the \theta_{23} intrinsic degeneracy, which must be resolved in order to achieve precision measurement of these two parameters. Spectral information around the vacuum oscillation maxima is shown to be the best way to resolve this degeneracy.