Construction of a Beam Test Prototype of the Hyper-K Water Cherenkov Detector to Control Systematic Errors for Leptonic CP Violation Measurements

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To achieve the full sensitivity of the Hyper-K experiment, it is necessary to control systematic uncertainties to the level of 2% or less. The primary sources of systematic error are on the modeling of the water Cherenkov detector, the modeling of the neutrino-nucleus interactions, and the modeling of neutrino production. Canadian collaborators have proposed a 1-kiloton scale water Cherenkov detector, the J-PARC E61 (NuPRISM) detector, located 1 km from the neutrino source at J-PARC to measure critical features of neutrino-nucleus interactions for Hyper-K. To achieve 2% systematic errors for Hyper-K, it is necessary to calibrate both Hyper-K and E61 to the level of 1%. Here, we propose a 30-ton water Cherenkov experiment to be placed in the Fermilab Test Beam Facility (FTFB) with particle momenta ranging from 100 MeV/c to 1200 MeV/c. This experiment will provide a test-bed for the calibration systems and photosensors that will be deployed in Hyper-K and E61. With a beam of known particle type, energy and trajectory, the calibration of the detector to the 1% level can be tested and improvements to the calibration systems can be made as necessary. Additionally, we will contribute to the EMPHATIC hadron production experiment already running in the FTBF, that will measure hadronic interaction processes that are necessary to provide the precise neutrino flux calculations necessary for the Hyper-K program.***The test beam program in the FTFB will be carried out as an international collaboration with Japan, the United States, the United Kingdom, Poland and Italy. The Canadian contribution is the development, testing and contruction of photosensors. The photosensor, developed by the Canadian collaboration, is a high resolution multi-PMT (photomultiplier tube) module that consists of 19 3 inch diameter fast PMTs in a pressure tolerant vessel. The PMTs view the detector through an acrylic window, and high voltage and readout electronics circuits are contained in the vessel. The first prototypes of the multi-PMT module, including the acrylic dome, vessel and electronics are being assembled and tested in 2018/2019 using an existing FY2018 RTI grant. Here, we propose to refine the design of the multi-PMT to achieve a production-ready design and build 30 of the multi-PMT modules for deployment in the test beam experiment.***In parallel, this grant will support the contribution to the EMPHATIC hadron production experiment that will characterize the hadron-nucleus interaction processes that are necessary to make precision calculations of neutrino production. EMPHATIC is an interantional collaboration between Japan, the United States and Canada, with each country providing sub-detectors. The design for an aerogel ring imaging Cherenkov detector has been developed by TRIUMF and University of Winnipeg and it will be built under this grant. This detector will provide particle identification in the forward direction for momenta up to 8 GeV/c.**