Measurement of the Flux and Zenith-Angle Distribution of Upward Through-Going Muons in Kamiokande II+III

The flux of upward through-going muons of minimum (mean) threshold energy $>1.6$ (3.0) GeV is measured, based on a total of 372 events observed by the Kamiokande $\mathrm{II}+\mathrm{III}$ detector during 2456 detector live days. The observed muon flux was ${\ensuremath{\Phi}}_{\mathrm{obs}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}[1.94\ifmmode\pm\else\textpm\fi{}0.10(\mathrm{stat}.{)}_{\ensuremath{-}0.06}^{+0.07}\mathrm{sys}.)]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}{\mathrm{cm}}^{\ensuremath{-}2}{\mathrm{s}}^{\ensuremath{-}1}{\mathrm{sr}}^{\ensuremath{-}1}$, which is compared to an expected value of ${\ensuremath{\Phi}}_{\mathrm{theo}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}[2.46\ifmmode\pm\else\textpm\fi{}0.54(\mathrm{theo}.)]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}{\mathrm{cm}}^{\ensuremath{-}2}{\mathrm{s}}^{\ensuremath{-}1}{\mathrm{sr}}^{\ensuremath{-}1}$. The observation is in agreement with the prediction within the errors. The zenith-angle dependence of the observed upward through-going muons supports the previous indication of neutrino oscillations made by Kamiokande using sub- and multi-GeV atmospheric neutrino events.