Superbeams plus Neutrino Factory: the golden path to leptonic CP violation

Abstract

Superbeams (SB) and Neutrino Factories (NF) are not alternative facilities for exploring neutrino oscillation physics, but successive steps. The correct strategy is to contemplate the combination of their expected physics results. We show its important potential on the disappearance of fake degenerate solutions in the simultaneous measurement of $\theta_{13}$ and leptonic CP violation. Intrinsic, sign($\Delta m_{13}^2$) and $\theta_{23}$ degeneracies are shown to be extensively eliminated when the results from one NF baseline and a SB facility are combined. A key point is the different average neutrino energy and baseline of the facilities. For values of $\theta_{13}$ near its present limit, the short NF baseline, e.g. L=732 km,becomes, after such a combination, a very interesting distance. For smaller $\theta_{13}$, an intermediate NF baseline of $O(3000$km) is still required.