Asymmetries of Secondary Cosmic Muons with High Statistics and Low   Systematics
  Project GRAND measures the asymmetries of secondary cosmic muons by calculating the differences between the muons from the east and the muons from the west for complete solar days. A similar north-south difference is also presented. These muons are identified in single track data taken with the 64 stations of Project GRAND; the data cover a two year span with a total muon sample of 30 billion muons. 
T. F. Lin, B. Fields, J. Gress, and J. Poirier