The Intermediate Water Cherenkov Detector for the Hyper-Kamiokande experiment

The Hyper-Kamiokande (HK) experiment will perform a broad physics program including the study of long-baseline neutrino oscillations. Following the successful T2K experiment, this will be achieved by detecting neutrinos produced at an upgraded 1.3 MW beam at the J-PARC with a far water Cherenkov detector with around 8 times larger detector volume than that of the Super-Kamiokande detector. To make full use of the high statistics data, an accurate prediction of neutrino interaction rates at the HK detector is essential. For this purpose, the Intermediate Water Cherenkov Detector (IWCD) is planned as one of HK's near detectors, using a kiloton scale water Cherenkov detector to be located around 1 km from the neutrino source at J-PARC. The unique feature of IWCD enables it to move vertically relative to the beam direction, changing the energies of neutrinos impinging the detector. By collecting data at various vertical positions, IWCD will study the relation between neutrino energy and products of neutrino interactions directly. This talk will describe the IWCD design and its physics program, including key technology, new photosensor module, and challenges for the IWCD measurements.