羊八井ARGO实验触发效率的地磁场效应

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

广延大气簇射(EAS)中次级带电粒子在地磁场中偏转,影响次级粒子的横向分布.本文简要分析了羊八井宇宙线观测站不同天顶角的地磁场因子随方位角的变化,表明地磁场对从北方来的宇宙线次级粒子横向分布的影响比对南方来的大.利用蒙特卡罗方法模拟了有无地磁场情况下两个大容量的EAS样本,采用ARGOG探测器模拟程序模拟羊八井ARGO阵列的触发效率.模拟结果表明在忽略地磁场影响时阵列的触发效率是各向同性的,有地磁场时触发效率南高于北,且原初粒子的天顶角越大,这种南北不对称性越明显.

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.