Abstract :
The first evidence for neutrino oscillation was obtained from zenith-angle distributions of atmospheric neutrinos observed by Super-Kamiokande. Recently, Super-Kamiokande has succeeded in observing the oscillation pattern in the event distribution as a function of L/E. This is the behavior expected from vacuum neutrino oscillations. Also, the first accelerator-based long baseline neutrino oscillation experiment, K2K, confirmed the atmospheric neutrino oscillation with a probability of no oscillation being 0.01%. From these experiments as well as other atmospheric neutrino experiments, a consistent picture of νμ↔ντ oscillation has been established. Near-future accelerator-based neutrino oscillation experiments aim at observing sub-dominant νμ↔νe oscillation in order to measure the mixing angle θ13.
