Letter of Intent: The Hyper-Kamiokande Experiment --- Detector Design and Physics Potential ---

We propose the Hyper-Kamiokande (Hyper-K) detectoras a next generation underground water Cherenkov detector. It will serve as a far detectorof a long baseline neutrino oscillationexperiment envisioned for the upgraded J-PARC, and as a detectorcapable of observing -- far beyond the sensitivity of the Super-Kamiokande(Super-K) detector-- proton decays, atmospheric neutrinos, and neutrinos from astronomical origins. The baseline design of Hyper-K is based on the highly successful Super-K, taking full advantage of a well-proven technology. (to be continued)