Present and Future Long Baseline Neutrino Experiment in Japan Takashi Kobayashi

The K2K experiment is the first accelerator-based long baseline neutrino experiment aiming to confirm the evidence of neutrino oscillation found in the atmospheric neutrino observation. The νµ beam of ∼1 GeV is produced at KEK and observed by Super-Kamiokande (SK) at 250 km distance. From June 1999 to June 2000, we have accumulated about 23 % of proposed number of protons on target. We observed 28 neutrino events in SK which originate at KEK. Expected number of events are 37.8+3.5−3.8. As a next generation experiment, we plan a neutrino oscillation experiment with baseline length of 295 km using 50 GeV PS in Japan Hadron Facility, which is approved last year, and SK. Using the ∼1 MW PS, we expect about 2 orders of magnitude higher neutrino flux than K2K. This high intensity beam enables us to determine oscillation parameters in νµ disappearance and explore νe appearance with unprecedented precision and reach. Current design of the neutrino facility and its physics potential are introduced.