Large-scale anisotropy of the cosmic-ray muon flux in Kamiokande

The large-scale anisotropy of cosmic-ray primaries in the celestial coordinate was studied using cosmic-ray muons recorded in a large water Cherenkov detector, Kamiokande. The right-ascension distribution of the muon arrival directions deviated from an isotropic distribution with a 2.8 standard deviation, and agreed well with the first harmonics with an amplitude of $(5.6\ifmmode\pm\else\textpm\fi{}1.9)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and a phase of $8.0\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}19.1\ifmmode^\circ\else\textdegree\fi{}$. This is the deepest underground observation of the large-scale anisotropy of cosmic rays, and agrees with observations with other underground experiments and extensive air-shower array experiments.