What can we learn about the lepton CP phase in the next 10 years?

A bstract We discuss how the lepton CP phase can be constrained by accelerator and reactor measurements in an era without dedicated experiments for CP violation search. To characterize globally the sensitivity to the CP phase δ CP , we use the CP exclusion fraction, which quantifies what fraction of the δ CP space can be excluded at given input values of θ 23 and δ CP . Using the measure we study the CP sensitivity which may be possessed by the accelerator experiments T2K and NO ν A. We show that, if the mass hierarchy is known, T2K and NO ν A alone may exclude, respectively, about 50%-60% and 40%-50% of the δ CP space at 90% CL by 10 years running, provided that a considerable fraction of beam time is devoted to the antineutrino run. The synergy between T2K and NO ν A is remarkable, leading to the determination of the mass hierarchy through CP sensitivity at the same CL.