物理学中的世纪难题：高能宇宙线的起源之“谜”*

  自从20世纪20年代宇宙线被发现以来，其起源问题一直为人们所困惑。这一未解之谜也因此被列入21世纪11大科学难题之中。在宇宙线起源的探寻中，不受磁场偏转影响的中性成分（如光子和中微子）很自然的成为宇宙线源头的信使。此外，通过测量受磁场影响微小的高能（>50 EeV）带电粒子，也可以获取源的信息。通过大量的实验研究，γ天文学取得了巨大成就，并有望破解世纪之谜。为了提高地面探测器的观测能力，发展宽视场和高灵敏度的巡天扫描探测手段有着至关重要的意义。位于中国西藏羊八井国际观测站的两个实验所采用的正是这种大气簇射的测量方法，它们分别是中意合作ARGO实验和中日合作ASγ实验。为获得更高灵敏度，笔者提出了在西藏羊八井建立集5种探测手段于一身的的大型复合实验阵列(LHAASO)。本文对宇宙线观测的发展历程以及前景做了详细介绍，在后半部分对LHAASO的物理背景和实验方案进行了详尽的阐述。

Unsolved Physics Puzzle in the Last Century: What Is Sources of High Energy Cosmic Rays

Since they were found in 1920’s, cosmic rays are investigated thoroughly for locating their sources. It is still one of 11 unsolved puzzles that drive people working hard in their own fields. Neutral components of the cosmic rays, photons and neutrinos are naturally selected as messengers between the source objects in the universe and us. It is also found that even if the ordinary charged cosmic ray particles can be used as such a messenger as long as their energies are sufficiently high, e.g. above 50 EeV. Large scale experiments in those fields form a frontier of a campaign for searching for the sources. Gamma ray astronomy seems to be the most successful and most likely to break through. In order to keep the strong momentum, a significant boost in sensitivity of survey observational power with wide field of view instrument is essential. The international observatory at Tibet, China has developed well with two major experiments, ARGO YBJ and ASγ, collaborating with Italy and Japan with the right techniques, namely air shower observation. We propose building a large complex array with five components at Yang Ba Jing, Tibet to boost the source survey sensitivity. Details about physics perspectives and tentative design are discussed in this paper.