利用羊八井联合观测开展宇宙线的多参数物理分析

Yangbajing Cosmic Ray Laboratory located at an altitude of 4300 m, is a good place for the ground detectors to measure the "knee". Two wide field-of-view Cherenkov telescopes have been successfully operated at Yangbajing Cosmic Ray Observatory near the ARGO-YBJ array since 2008; and a few millions of coincident cosmic ray events have been measured. It is well-known that a uniform and robust shower energy measurement could be expected because the Cherenkov signal accumulates all photons produced by shower electrons at all stages of the shower longitudinal development. The ARGO-YBJ experiment is possessed of both the full coverage in the array and the high altitude which allow the measurement to reach the lowest energy threshold on the ground. The precise energy spectrum of cosmic ray and composition will be measured by taking advantages from two detectors. It also has an opportunity for EAS experiments to study the system uncertainty well by directly comparing the results with the direct measurement. The composition and energy spectra in the "knee " region can be accurately measured by carrying out the project.

羊八井宇宙线观测站位于海拔4300m，是地面探测器测量"膝"区宇宙线粒子的绝佳位置。两台广角契伦科夫望远镜从2008年开始在羊八井宇宙线观测站稳定运行，已经获得几百万和ARGO-YBJ实验符合的宇宙线事例。契伦科夫望远镜可以直接测量宇宙线空气簇射的纵向发展，具有量能器的性质。ARGO-YBJ实验拥有全覆盖的RPC探测器阵列，是目前世界上测量空气簇射横向发展最精确的探测器。结合这两种探测器的优点，开展宇宙线多参数粒子鉴别和能谱测量具有显著的优势。探测器位于高海拔，还可实现低阈能宇宙线能谱测量；宇宙线能谱在低能段和直接精确测量结果重合；通过对比，准确研究地面实验的系统误差。通过本项目的开展，可以精确测量"膝"区宇宙线的成分和能谱。

极高能宇宙线能谱上的结构如“膝”反应了宇宙线的起源、加速及传播机制，精确测量能谱拐折的位置和拐折的精细结构具有非常重要的物理意义。望远镜样机和ARGO-YBJ实验位于海拔4300米的西藏羊八井国际宇宙线观测站，非常适合“膝”区宇宙线成份能谱精确测量。项目组利用望远镜样机和ARGO-YBJ实验符合宇宙线事例完成了100TeV-3PeV的宇宙线质子+氦核能谱测量，该结果跨越了直接测量结果（CREAM气球实验）和地面其它实验结果（KASCADE实验和Tibet实验），同时也和CREAM的轻成份能谱结果很好地吻合，为在“膝”区利用直接测量结果标定地面实验测量结果奠定基础，并首次在700 TeV处发现了非常重要的质子+氦核能谱“膝”，远低于人们根据之前实验结果或理论模型推断的结果，在国际宇宙线界，该成果已引起了大家的广泛关注。该成果发表在Physics Review D上。.开展利用LHAASO实验广角切伦科夫望远镜测量到的直射契伦科夫光，鉴别100TeV以下的宇宙线铁核和重建铁核的能量。分析结果表明利用直射契伦科夫光重建得到的宇宙线能量相对于利用簇射粒子或切伦科夫光重建得到的能量有更小的系统误差；提高望远镜的像素空间分辨率可以提高成分的鉴别能力。该成果发表在Astroparticle Physics上。

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