2～7 GeV高亮度正负电子对撞机的物理研究

Physics on the high intensive electron position accelerator at 2–7 GeV

经过几十年的实验检验,标准模型被认为是描述自然界微观世界最成功的理论模型.特别是随着2012年Higgs粒子的发现,标志着人类对物质微观世界的认识达到了空前的高度.尽管如此,仍存在一系列标准模型不能解决的基本问题,如暗物质和暗能量的本质、宇宙正反物质的不对称、夸克和轻子的分代和引力作用的描述等.另外,作为标准模型的两个组成部分之一,量子色动力学在高能量区得到了实验的精确检验,但是在低能区仍存在许多重大的科学问题,亟待实验和理论进一步发展和完善.因此,我们亟待进行超出现有水平的实验来更深入地探索微观物质结构,揭示微观世界的更多奥秘.本文阐述在t-粲能区有待解决的重大前沿科学问题,以及在中国建设新一代的2~7 GeV能区高亮度(0.5×10^(35)~1.0×10^(35) cm^(-2) s^(-1))正负电子加速器的可行性和必要性.

With the experimental examination in the past few decades, the Standard Model（SM, which describes the building blocks of matter and the fundamental forces in the universe, is considered to be the most successful theoretical model to describe the subatomic world. In particular, after the discovery of Higgs particle in 2012 at Large Hadron Collider（LHC, the success of SM reaches to an unprecedented level. However, it does leave a lot of phenomena unexplained questions, such as, what are the dark matter and dark energy？ what happened to the anti-matter matter asymmetric in the world？ why are there three generations of quarks and lepton with such a different mass scale？ and so on. At present, it is believed that there exists a more general theory hidden deeply in the subatomic world, which includes the new physics, and can solve the all unexplained questions, and the SM is its appromiximation in the current reached energy region experimentally. On the other hand, as one of two parts of SM, Quantum chromodynamics（QCD theory, which is theory of strong interactions, a fundamental force describing the interactions between quarks and gluons, and have been tested precisely in the high energy range, but there is still some fundamental questions unsolved in row energy region. Therefore, it is urgent for us to have the experiments beyond current level to explore and reveal the mysteries of the subatomic world. At present, the studies of particle physics based on accelerator is one of most powerful approach to investigate the subatomic world, and can be classed into two frontiers, i.e. the high energy frontiers and the high-intensitive fronitiers. A super tau-charm factory, which is expected to have luminosity of 0.5×10^35–1.0×10^35 cm^-2s^-1 and with center of mass energy at 2–7 GeV, is one of typical high intersitive frontiers experiment. It can produce all there generation leptons and first and secondary generation quarks and have several unique features, e.g., running on the energy at the transition between the perturbative and non-perturbative QCD, producing rich resonances, charmonium and charmed mesons, having threshold characteristics which provides clean environment for the signals, etc. The super tau-charm factory is regarded as an ideal platform to explore the hadronic physics and search for the new physics beyond the SM. In this letter, we present the key science questions and physics topics are desired on a super tau-charm factory, and discuss the feasibility and necessity to build a new generation high intensive Electron Position Accelerator Facility（HIEPA at 2–7 GeV in China. The current international and internal situations for particle physics progress, the key technologies in both accelaerator and detector, and the driving force for science and technology to build the tau-charm factory in China are also illustrated. We conclude that HIEPA is an excellent option from all aspects for the future accelerator programs in China based on its current scale of particle physics community and the expertise reserve, and call for the start and support from the government of RD for this project.