Evidence for an Oscillatory Signature in Atmospheric Neutrino Oscillations

Muon neutrino disappearance probability as a function of neutrino flight length $L$ over neutrino energy $E$ 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 ${\nu }_{\mu }\leftrightarrow {\nu }_{\tau }$ neutrino oscillation parameters; $1.9\times {10}^{-3}<\Delta m^2<3.0\times {10}^{-3}{\mathrm{e}\mathrm{V}}^2$ and ${sin}^{2}2\theta >0.90$ at 90% confidence level.