Exploring Leptonic CP Violation by Reactor and Neutrino Superbeam Experiments

We point out the possibility that reactor measurement of theta_{13}, when combined with high-statistics nu_e appearance accelerator experiments, can detect leptonic CP violation. Our proposal is based on a careful statistical analysis under reasonable assumptions on systematic errors, assuming 2 years running of the neutrino mode J-PARC -> Hyper-Kamiokande experiment and a few years running of a reactor experiment with 100 ton detectors at the Kashiwazaki-Kariwa nuclear power plant. We show that the method can be arranged to be insensitive to the intrinsic parameter degeneracy but is affected by the one due to unknown sign of Delta m^2_{31}.