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 $>1.6\mathrm{}$ (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 ${\Phi }_{\mathrm{obs}}=[1.94\pm 0.10(\mathrm{stat}.\mathrm{}{)}_{-0.06\mathrm{}}^{+0.07\mathrm{}}\mathrm{sys}.\mathrm{}\left)\right]\times {10}^{-13\mathrm{}}{\mathrm{cm}}^{-2\mathrm{}}{\mathrm{s}}^{-1\mathrm{}}{\mathrm{sr}}^{-1\mathrm{}}$, which is compared to an expected value of ${\Phi }_{\mathrm{theo}}=[2.46\pm 0.54(\mathrm{theo}.\mathrm{}\left)\right]\times {10}^{-13\mathrm{}}{\mathrm{cm}}^{-2\mathrm{}}{\mathrm{s}}^{-1\mathrm{}}{\mathrm{sr}}^{-1\mathrm{}}$. 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.