The Hyper-Kamiokande experiment is a proposed next generation underground water Cherenkov detector. The baseline design of Hyper-Kamiokande is based on the highly successful Super-Kamiokande experiment, taking full advantage of a well-proven technology. It will serve as the far detector of a long baseline neutrino oscillation experiment envisioned for the upgraded J-PARC beam, and as a detector capable of observing -far beyond the sensitivity of the Super-Kamiokande detector -proton decays,

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... spheric neutrinos, and neutrinos from astronomical origins. Assuming a total exposure of 7.5 MW × 10 7 sec integrated proton beam power (corresponding to 1.56 × 10 22 protons on target with a 30 GeV proton beam) to a 2.5-degree off-axis neutrino beam, it is expected that the leptonic CP phase δ CP can be determined to better than 19 degrees for all possible values of δ CP , and CP violation can be established with a statistical significance of more than 3 σ (5 σ ) for 76% (58%) of the δ CP parameter space. Using both ν e appearance and ν µ disappearance data, the expected 1σ uncertainty of sin 2 θ 23 is 0.015(0.006) for sin 2 θ 23 = 0.5(0.45).