Evidence for an Oscillatory Signature in Atmospheric Neutrino Oscillations

Muon neutrinodisappearance probability as a function of neutrinoflight length L over neutrinoenergy E was studied. A dip in the L/E distribution was observed in the data, as predicted from the sinusoidal flavor transition probability of neutrino oscillation. The observed L/E distribution constrained nu_mu nu_tau neutrino oscillationparameters; 1.9x10^-3 0.90 at 90% confidence level.