Measurement of the Flux and Zenith-Angle Distribution of Upward Throughgoing Muons by Super-Kamiokande

A total of 614 upward throughgoing muons of minimum energy 1.6 GeV are observed by Super-Kamiokande during 537 detector live days. The measured muon flux is [1.74+/-0.07\(stat\)+/-0.02\(sys\)]×10^-13 cm^-2 s^-1 sr^-1 compared to an expected flux of [1.97+/-0.44\(theor\)]×10^-13 cm^-2 s^-1 sr^-1. The absolute measured flux is in agreement with the prediction within the errors. However, the zenith-angle dependence of the observed upward throughgoing muon flux does not agree with no-oscillation predictions. The observed distortion in shape is consistent with the ν_μ<-->ν_τ oscillation hypothesis with ²2θ>0.4 and 1×10^-3<Δm²<1×10^-1 eV² at 90% confidence level.