Azimuthal angular dependence study of the atmospheric muon charge ratio at sea level using Geant4

Abstract

The azimuth dependence of the cosmic muon charge ratio at sea level was estimated using the Geant4 simulation package. Simulations were separately run at 12 azimuth angles ranging from 0 degrees to 330 degrees with 30 degrees increment. Two hundred thousand proton and alpha particles were randomly distributed over the zenith angle range 30 degrees < theta < 40 degrees at each azimuth angle. The kinetic energy spectra of proton and helium nuclei were taken from the balloon-flight measurements. The atmospheric muon charge ratio was calculated at each azimuthal angle for low energy muons with a mean momentum around 0.5 GeV/c. The Geant4 simulation results have been compared with those of the CORSIKA simulation program and with the WILLI measurements. The simulation results reproduce well the measured east-west effect with a non-zero asymmetry A(EW) = 0.24. This asymmetry in the charge ratio decreases from 0.37 to 0.19 as the momentum increases from 0.22 to 0.70 GeV/c.