Resolving Eight-Fold Neutrino Parameter Degeneracy by Two Identical Detectors with Different Baselines

Abstract

We have shown in a previous paper that two identical detectors with each fiducial mass of 0.27 megaton water, one in Kamioka and the other in Korea, which receive the (anti-) muon neutrino beam of 4 MW power from J-PARC facility have potential of determining the neutrino mass hierarchy and discovering CP violation by resolving the degeneracies associated with them. In this paper, we point out that the same setting has capability of resolving the \theta_{23} octant degeneracy in region where sin^2 2\theta_{23} \lsim 0.97 at 2 standard deviation confidence level even for very small values of \theta_{13}. Altogether, it is demonstrated that one can solve all the eight-fold neutrino parameter degeneracies in situ by using the Tokai-to-Kamioka-Korea setting if \theta_{13} is within reach by the next generation superbeam experiments. We also prove the property called ``decoupling between the degeneracies'', which is valid to first order in perturbation theory of the earth matter effect, that guarantees approximate independence between analyses to solve any one of the three different type of degeneracies.