Current Status of the K2k Long-baseline Neutrino-oscillation Experiment

The K2K (KEK to Kamioka) long-baseline neutrino-oscillation experiment was successfully started in early 1999. A total intensity of 7.20 × 10 protons on target, which is about 7% of the goal of the experiment, was accumulated in 39.4 days of data-taking in 1999. We obtained 3 neutrino events in the fiducial volume of the Super-Kamiokande detector, whereas the expectation based on observations in the front detectors is 12.3 −1.9 . An analysis of oscillation searches from the view points of absolute event numbers, distortion of neutrino energy spectrum, and νe/νμ ratio is in progress.