Physics potential of the Tokai-to-Kamioka-and-Korea proposal: An extension of the Tokai-to-Kamioka neutrino oscillation experiment with a far detector in Korea

Abstract

We study the 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 Tokai-to-Kamioka 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 water \ifmmode \check{C}\else \v{C}\fi{}erenkov detector is placed at various locations in Korea for the off-axis beam (OAB) of 2.5\ifmmode^\circ\else\textdegree\fi{} and 3.0\ifmmode^\circ\else\textdegree\fi{} at the Super-Kamiokande site. The best results are found for a combination of 3.0\ifmmode^\circ\else\textdegree\fi{} OAB at SK ($L=295\text{ }\text{ }\mathrm{km}$) and 0.5\ifmmode^\circ\else\textdegree\fi{} OAB at $L=1000\text{ }\text{ }\mathrm{km}$, where the mass hierarchy pattern can be determined at $3\ensuremath{\sigma}$ level for ${sin}^{2}2{\ensuremath{\theta}}_{\mathrm{RCT}}\ensuremath{\gtrsim}0.05$ (0.06) when the hierarchy is normal (inverted), after 5 yr of running ($5\ifmmode\times\else\texttimes\fi{}{10}^{21}\text{ }\text{ }\mathrm{POT}$). We also find that the leptonic $CP$ phase, ${\ensuremath{\delta}}_{\mathrm{MNS}}$, can be constrained uniquely, without invoking antineutrino beams, as long as the mass hierarchy pattern is determined. Those results are obtained by assuming that the charged current quasielastic 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.