Isotropy of cosmic rays with energies 5 TeV to 100 TeV

Abstract

A cosmic-ray isotropy measurement was carried out using about 10$sup 6$ underground muon events. The directional properties of the detector allowed events to be separated into bins according to the depth of rock penetrated and the celestial angles of the primary particles. The result at a median primary energy of 12 TeV, for muons penetrating an average depth of 2.9 x 10$sup 5$ g cm$sup -2$, was a diurnal anisotropy of (0.1 +- 0.2) %. No single 10 degree x 10 degree angular bin showed a significant excess of particles. The deviation from the expected numbers per bin showed a normal distribution with standard deviation no larger than that expected from counting statistics. This allowed a limit to be set on the angular roughness of the cosmic-ray flux. (AIP)