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

Abstract

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 ´ 1035–1.0 ´ 1035 cm - 2 s - 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 R&D for this project.