Solving the degeneracy of the lepton-flavor mixing angle theta(ATM) by the T2KK two detector neutrino oscillation experiment

If the atmospheric neutrino oscillation amplitude, sin(2) 2 theta(ATM) is not maximal, there is a two fold ambiguity in the neutrino parameter space: sin(2) theta(ATM) > 0.5 or sin(2) theta(ATM) < 0.5. In this article, we study the impact of this degeneracy, the so-called octant degeneracy, on the T2KK experiment, which is a proposed extension of the T2K (Tokai-to-Kaimoka) neutrino oscillation experiment with an additional water Cerenkov detector placed in Korea. We find that the degeneracy between sin(2) theta(ATM) = 0.40 and 0.60 can be resolved at the 3 sigma level for sin(2) 2 theta(RCT) > 0.12 (0.08) for the optimal combination of a 3.0 degrees off-axis beam (OAB) at SK (L = 295km) and a 0.5 degrees OAB at L = 1000km with a far detector of 100kton volume, after 5 years of exposure with 1.0 (5.0) x 10(21) POT/year, if the hierarchy is normal. We also study the influence of the octant degeneracy on the capability of T2KK experiment to determine the mass hierarchy and the leptonic CP phase. The capability of rejecting the wrong mass hierarchy grows with increasing sin(2) theta(ATM) when the hierarchy is normal, whereas it is rather insensitive to sin(2) theta(ATM) for the inverted hierarchy. We also find that the 1 sigma allowed region of the CP phase is not affected significantly even when the octant degeneracy is not resolved. All our results are obtained for the 22.5 kton Super-Kamiokande as a near detector and without an anti-neutrino beam.