宇宙线大气簇射μ子定点密度及原初能谱“膝”的研究

Study of EAS Local Muon Density Spectrum and the Knee in the Energy Spectrum of Primary Cosmic Rays

用梁王山宇宙线观测站的数据研究宇宙线大气簇射 μ子定点密度谱 ,谱呈现明显的拐折 .通过MonteCarlo模拟 ,得到拐点对应的能量约为 1.7× 10 15eV ,拐点前后原初能谱指数差约为 0 .4 3,证实了KASCADE实验 μ子定点密度谱呈现拐折的首次观测结果 ,又一次推证了原初宇宙线能谱膝的存在 .

With the extensive air shower (EAS) array at Mt. Liang Wang (735 g·cm2,245°N,102.9° E,Kunming China) it is able to measure the muon density spectrum at a fixed distance from the core of EAS in the knee region. The spectra at two different fixed core distances (25m≤core distance<30m,30m≤core distance<35m) were obtained from 4.4×104 events collected in 1994 with criteria 5×104≤ size≤1.6×107 and 10°≤θ<30° that show obvious kinks. Monte Carlo simulations for the EAS development and detection with same selection criteria in the array triggering and the analysis procedure have been performed in order to relate the local muon densities to primary energy. As a result,we have deduced that the average position of the knee (E knee) is at about 1.7×10 15eV and the average difference of the slopes of the primary energy spectrum before and after the knee (Δγ) is about 0.43. This work corroborates the first result (E knee=5PeV,Δγ=0.3) reported by KASCADE. It authenticates reliably the existence of the knee at the primary energy spectrum by another composition of EAS - muon composition (more direct than electron composition). Based on the results obtained by two experiments,the difference of slopes of cosmic ray primary energy spectrum before and after the knee is close to 0.4 that is accepted widely,while the energy of the knee is different from the accepted 3PeV.