Background study on V_e appearance in a very long baseline neutrino oscillation experiments with a large water Cherenkov detector

There is a growing interest in very long baseline neutrino oscillation as a machinery to probe the last three unmeasured neutrino oscillation parameters: the mixing angle sin²2θ₁₃, the possible CP violating phase δ_CP and the mass hierarchy, namely, the sign of Δm² ₃₂. Despite very successful performance of water Cherenkov detectors such as IMB, Kamiokande and Super-Kamiokande, it is not well known that this detector technology can also provide required performance for a next generation of long baseline neutrino oscillation experiment. This report presents the latest effort to prove that a large water Cherenkov detector will be adequate for rather difficult task of detecting V_e s from the neutrino oscillation vμ ! V_e effciently over a potentially large background from γ s from π⁰ produced by neutral current.