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 $(5.6\mathrm{}\pm 1.9)\times {10}^{-4}$ and a phase of $8.0°\pm 19.1°$. 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.