BEXCO - Room D(109/110)
[NU072] An intermediate water Cherenkov detector for the Hyper-Kamiokande experiment: overview and status
The proposed Hyper-Kamiokande (Hyper-K) is a next generation underground large water Cherenkov (WCh) detector. It has a broad program of physics and astrophysics mainly focusing on the precise measurement of the lepton mixing matrix and the leptonic CP asymmetry. Hyper-K will act as a far detector to measure the oscillated neutrino flux from the long-baseline neutrino experiment using 0.6 GeV neutrinos produced by a 1.3 MW proton beam at J-PARC in Japan. To minimise systematic uncertainties an intermediate WCh detector has been proposed. The intermediate detector will use a new technique to enhance its performance, neutron tagging. The water in the tank will be doped with Gd that allows to tag neutrons. Tagging events by the presence and number of final-state neutrons provides a unique capability to discriminate between different (anti)neutrino interactions reducing the error of the Hyper-K measurements. In addition to the neutrino oscillation experiment Hyper-K and the intermediate detector will study atmospheric neutrinos, proton decay and neutrinos from astrophysical sources such as supernova. Neutron tagging in the intermediate detector can significantly reduce backgrounds in proton decay and supernova neutrinos searches. These studies will already be starting by the existing Super Kamiokande experiment which plans to dope the water in the tank with Gd in 2018. The final state neutron multiplicities that will be used in the atmospheric and proton decay analyses need to be measured with a well understood neutrino source. For this, the neutrino beam from J-PARC in the intermediate water Cherenkov detector will be used. We will discuss the expected physics reach and the status of the intermediate detector focusing on the benefits from neutron tagging in beam neutrinos, proton decay, atmospheric and supernova neutrinos measurements.