No abstract

We study physics potential of placing a far detector in the east coast of Korea, where the off-axis neutrino beam from J-PARC at Tokai village for the T2K project has significant intensity at a few GeV range. In particular, we examine the capability of determining the mass hierarchy pattern and the CP phase of the lepton-flavor-mixing matrix when a 100 kt waterČerenkov detector is placed at various locations in Korea for the off-axis beam (OAB) of 2.5 • and 3.0 • at the Super-Kamiokande site. The best results are found for a combination of 3.0 • OAB at SK (L = 295km) and 0.5 • OAB at L = 1000km, where the mass hierarchy pattern can be determined at 3-σ level for sin 2 2θ RCT > ∼ 0.05 (0.06) when the hierarchy is normal (inverted), after 5 years of running (5 × 10 21 POT). We also find that the leptonic CP phase, δ MNS , can be constrained uniquely, without invoking anti-neutrino beams, as long as the mass hierarchy pattern is determined. Those results are obtained by assuming that the charged current quasi-elastic events can be separated from the other backgrounds with high efficiency, the neutrino energy can be reconstructed with a hundred MeV uncertainty, and the earth matter density along the baseline can be determined with 3% accuracy. *

We study the earth matter effects in the Tokai-to-Kamioka-and-Korea experiment (T2KK), which is a proposed extension of the T2K (Tokai-to-Kamioka) neutrino oscillation experiment between J-PARC at Tokai and Super-Kamiokande (SK) in Kamioka, where an additional detector is placed in Korea along the same neutrino beam line. By using recent geophysical measurements, we examine the earth matter effects on the oscillation probabilities at Kamioka and Korea. The average matter density along the Tokai-to-Kamioka baseline is found to be 2.6 g/cm 3 , and that for the Tokai-to-Korea baseline is 2.85, 2.98, and 3.05 g/cm 3 for the baseline length of L-= 1000, 1100, and 1200 km, respectively. The uncertainty of the average density is about 6%, which is determined by the uncertainty in the correlation between the accurately measured sound velocity and the matter density. The effect of the matter density distribution along the baseline is studied by using the step function approximation and the Fourier analysis. We find that the ν µ → ν e oscillation probability is dictated mainly by the average matter density, with small but non-negligible contribution from the real part of the first Fourier mode. We also find that the sensitivity of the T2KK experiment on the neutrino mass hierarchy does not improve significantly by reducing the matter density error from 6% to 3%, since the measurement is limited by statistics for the minimum scenario of T2KK with SK at Kamioka and a 100 kt detector in Korea considered in this report. The sensitivity of the T2KK experiment on the neutrino mass hierarchy improves significantly by splitting the total beam time into neutrino and anti-neutrino runs, because the matter effect term contributes to the oscillation amplitudes with the opposite sign. *

The T2K neutrino oscillation experiment will start in 2009. In this experiment the center of the neutrino beam from J-PARC at Tokai village will go through underground beneath Super-Kamiokande, reach the sea level east of Korean shore, and an off-axis beam at 0.5 • to 1.0 • can be observed in Korea. We study physics impacts of putting a 100 kt-level WaterČerenkov detector in Korea during the T2K experimental period. For a combination of the 3 • off-axis beam at SK with baseline length L = 295km and the 0.5 • off-axis beam in the east coast of Korea at L = 1000km, we find that the neutrino mass hierarchy (the sign of m 2 3 − m 2 1 ) can be resolved and the CP phase of the MNS unitary matrix can be constrained uniquely at 3-σ level when sin 2 2θ rct >