GEANT4 SIMULATION FOR THE ZENITH ANGLE DEPENDENCE OF COSMIC MUON INTENSITIES AT TWO DIFFERENT GEOMAGNETIC LOCATIONS

Abstract

The zenith angle dependence of cosmic muon flux at sea level in the western, eastern, southern and northern azimuths have been investigated separately for Calcutta, India and Melbourne, Australia for muon momenta up to ~500 GeV /c using Geant4 simulation package. These two locations were selected due to the fact that they significantly differ in geomagnetic cutoff rigidity. The exponent n, which is defined by the relation I(θ) = I(0°) cos nθ, was obtained for each azimuth in Calcutta and Melbourne. By acquiring an agreement between the simulation results and the experimental ones, the simulation study was extended for different azimuth angles and higher muon momenta. It was shown that the angular dependence of the cosmic muon intensity decreases with the increase of muon momentum at both locations. Moreover, the exponent becomes independent of both geomagnetic location and the azimuth angle for muons with momentum above 10 GeV /c, and it is nearly zero above 50 GeV /c. Therefore, it can be concluded that the cosmic muons with momenta between 50 GeV /c and ~500 GeV /c reach the sea level almost isotropically.