The Mayflower Mine muon detector's search for periodic changes in the cosmic-ray flux over a 5.4-year period has obtained a 4.4-Hz muon rate from primary cosmic rays with a median rigidity of 1.5 trillion V. Fourier transformation of the observational data yields sidereal frequency peak, anisotropy, and second and third harmonic data; these combine to yield a minimum when the detector 'points' toward the north Galactic pole, and a broad maximum when its sensitive direction is close to the Galactic plane.
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Cutler et al. (1991) studied this question.