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 \nu_\mu <-> \nu_\tau oscillation hypothesis with \sin^22\theta > 0.4 and 1x10^{ -3} < \Delta m^2 < 1x10^{ -1} eV^{ 2} at 90% confidence level.
Categories: hep-ex