Recent results from the K2K experiment

Since 1999, the KEK to Kamioka long-baseline neutrino experiment (K2K) has begun its investigation of neutrino oscillations suggested by atmospheric neutrino observations. Until July 2001, we have accumulated 4.8 x 1019 protons on target and observed 56 in-fiducial events at Super-Kamiokande detector, which is located 250km from KEK. The expected number of events is estimated to be 80.1-5.4+6.2. We fit the neutrino oscillation parameters by using the observed number of events and measured energy spectrum of neutrinos. The probability to observe only 56 events and such an energy spectrum due to statistical fluctuation is less than 1%. Also, the favored oscillation parameter region agrees well with the one suggested by the atmospheric neutrino experiments