Multi-PMT development for the Hyper-Kamiokande project

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In this RTI grant request, we propose to build the first working prototype and establish the production process of multi-PMT (mPMT) modules for E61(NuPRISM) and Hyper-Kamiokande water Cherenkov detector projects. Large water Cherenkov detectors, which were first built to search for proton decay, led to the discovery of neutrinos from supernova 1987A, solar neutrino oscillations, atmospheric neutrino oscillations, and long baseline neutrino oscillations. This proposal is for the development of a photosensor module which will lead to a major Canadian contribution to the next generation large water Cherenkov detector, Hyper-Kamiokande (HK).******The Canadian group has developed a new concept for a water Cherenkov near detector, E61 (NuPRISM) for HK. The detector spans a wide range of off-axis angles to sample neutrino fluxes with different spectra from the same source. By linear combination of the events at different off-axis positions the neutrino cross section can be studied precisely. With an order of magnitude larger fiducial mass than the current Super-Kamiokande (SK) detector and E61(NuPRISM) near Water Cherenkov, HyperK can observe CP violation at better than 5σ significance for a wide range of the CP violating phase δcp and further explore if the atmospheric neutrino mixing (θ23) is maximal. The long baseline neutrino study is complemented by the atmospheric neutrino samples of HK with a much wider range of baseline up to the size of the earth. HK also expands the sensitivities for proton decays and neutrino astrophysics such as solar and supernova neutrinos, and the search for dark matter.******The photosensor array proposed for E61 (NuPRISM) is called a multi-PMT (mPMT). It is an integrated module consisting of 26 3-inch PMTs inside a 20-inch diameter vessel, 19 looking into the detector volume and 7 facing the veto region. The fine granularity and the better timing resolution are essential for a smaller water Cherenkov detector due to the smaller image of the Cherenkov ring. The mPMT can significantly improve the event reconstruction of HK and is considered as part of its photodetector system as well.******In summer 2017, HK project was selected to be on the road map of the Japanese funding agency (MEXT), and a new HK institute is started at University of Tokyo for the HK construction. The full funding approval is expected in a year or two. At its September 2017 collaboration meeting, E61 (NuPRISM) adapted a staged detector con- struction strategy. A 3-4m diameter charged beam test prototype, which uses 150 mPMTs, will be constructed in 2019-2021. The beam test is followed by the full E61(NuPRISM), the water Cherenkov near detector at HK using 500 mPMTs. The E61(NuPRISM) mPMT construction will be directly followed by a production of a few thousand mPMTs for HK in time of the installation in HK tank in 2025. The mPMT development in this proposal will provide key development to open up the exciting future in neutrino physics.