Evidence for neutrino oscillations in atmospheric neutrino observations on behalf of the Super-Kamiokande and Kamiokande Collaborations

We present the results of atmospheric neutrino observations in large water Cherenkov detectors, Super-Kamiokande and Kamiokande. Compared with detailed calculations of atmospheric neutrino fluxes, these data exhibit the large deficit of upward going muon neutrinos while electron neutrinos are observed as expected. Any combination of experimental biases and calculation uncertainties cannot explain the data. However, this phenomenon can be well interpreted as muon neutrino oscillations and we obtain the allowed region of oscillation parameters as 10−3 eV2<Δm2<10−2 eV2 and sin2 2θ>0.8 at 90% confidence level.