The K2K long-baseline neutrino oscillation experiment has analyzed all data including the period ending in February 2004. The total data sample is from 8.9 × 1019 protons on target. We observe 108 events at the far detector, Super-Kamiokande, when 150.9 +11.6 -10.0 were expected. Further, we observe a distortion of the neutrino energy spectrum which is consistent with νμ to ντ oscillation. The probability that we would observe these results if there is no neutrino oscillation is 0.011%, a 3.9 σ significance.
- Neutrino oscillation