Status of K2K experiment

The KEK to Kamioka long-baseline neutrino experiment (K2K) has begun its investigation of neutrino oscillations. Twenty-eight neutrino events have been detected in coincidence with expected arrival time of the beam in the 22.5kt fiducial volume of Super-Kamiokande, the far detector at 250 km distance. The expectation is 37.8−3.8+3.5, derived using measurements of neutrino interactions in a near detector and extrapolation using a beam simulation validated by a measurement of pion kinematics after production and focusing. The background is of order 10−3 events.