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 $[1.74\ifmmode\pm\else\textpm\fi{}0.07(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.02(\mathrm{sys})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}{\mathrm{cm}}^{\ensuremath{-}2}{\mathrm{s}}^{\ensuremath{-}1}{\mathrm{sr}}^{\ensuremath{-}1}$ compared to an expected flux of $[1.97\ifmmode\pm\else\textpm\fi{}0.44(\mathrm{theor})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}{\mathrm{cm}}^{\ensuremath{-}2}{\mathrm{s}}^{\ensuremath{-}1}{\mathrm{sr}}^{\ensuremath{-}1}$. 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 ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ oscillation hypothesis with ${sin}^{2}2\ensuremath{\theta}>0.4$ and $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}<\ensuremath{\Delta}{m}^{2}<1\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}1}{\mathrm{eV}}^{2}$ at 90% confidence level.