Monte Carlo Study for the Effect of Geomagnetic Field on Trigger Efficiency of ARGO-YBJ Experiment

The deflection of the secondary charged particle trajectories of EAS in the geomagnetic field distorts the lateral distribution of the secondaries. The variation of the geomagnetic effect with the azimuthal angle in different zenith angle intervals for YBJ-ARGO experiment is studied using Monte Carle simulation. The geomagnetic field leads to a stretched lateral distribution of the secondaries, thus both the density of the secondaries near the shower axis and the trigger efficiency of the array decrease. This effect is larger for the showers coming from the north than that from the south, such that the trigger efficiency for the former is lower than that for the latter. The north-south asymmetry becomes more evident with larger zenith angles.