Measurement of the flux and zenith-angle distribution of upward through-going muons by Super-Kamiokande

Abstract

A total of 614 upward through-going 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.)x10^{-13}cm^{-2}s^{-1}sr^{-1} compared to an expected flux of 1.97+/-0.44(theo.)x10^{-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 through-going muon flux does not agree with no-oscillation predictions. The observed distortion in shape is consistent with the ν_μ<-> ν_τoscillation hypothesis with \sin^22θ> 0.4 and 1x10^{-3} < Δm^2 < 1x10^{-1} eV^{2} at 90% confidence level.