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 II+III detector during 2456 detector live days. The observed muon flux was ${{Φ}}obs{{0ex}{0ex}}={{0ex}{0ex}}[1.94±{}0.10(stat.{)}_{{-}0.06}+0.07sys.)]×{}{10}^{{-}13}{cm}^{{-}2}{s}^{{-}1}{sr}^{{-}1}$, which is compared to an expected value of ${{Φ}}ₜₕₑₒ{{0ex}{0ex}}={{0ex}{0ex}}[2.46±{}0.54(theo.)]×{}{10}^{{-}13}{cm}^{{-}2}{s}^{{-}1}{sr}^{{-}1}$. 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.