A Water Cherenkov Test Beam Experiment for Hyper-Kamiokande and Future Large-scale Water-based Detectors

Water Cherenkov and water-based particle detector technologies are used to realize multi-kiloton scale experiments such as the currently operating Super-Kamiokande experiment, the planned Hyper-Kamiokande experiment and the proposed THEIA detector and ESSnuSB detectors. These experiments are operated or proposed to study a broad range of physics including neutrino oscillations, nucleon decay, dark matter and neutrinoless double beta decay. The neutrino oscillations program will also include kiloton scale near or intermediate detectors used to study neutrino production and interactions in the absence of neutrino oscillations, such as the Hyper-K Intermediate Water Cherenkov Detector (IWCD). Realization of these physics programs will require new detector technologies and percent level calibration of detector responses and models of physics processes within the detector. Here we describe our intent to propose a 50~ton scale Water Cherenkov test experiment (WCTE) to be deployed in a North or East test beam experimental area. The experiment will include a secondary target located just upstream of the experiment in order to produce very low energy particle fluxes, including charged pions. The WCTE program will be carried out with the following objectives: - Operate and understand the performance of new detector technologies such as multi-PMTs, dichroicon wavelength-separating cones and water-based liquid scintillator in a fully integrated detector. - Study the performance of a <1 kiloton scale water Cherenkov detector with known particle fluxes, and test and develop calibration systems necessary for accurate modeling of a detector of this size. - Measure important physics processes for the modeling of water Cherenkov detector responses, including high-angle Cherenkov light production, pion scattering and absorption, and secondary neutron production in hadron scattering. We aim to start operation of the water Cherenkov test experiment in 2021-2022