报告摘要：High-energy nuclear collisions provide us a unique tool to study the QCD phase diagram in the laboratory. At both RHIC (Au+Au collisions at √sNN = 200 GeV) and LHC (Pb+Pb collisions at √sNN = 2.76 TeV), a new form of matter, the strongly coupled quark-gluon plasma (sQGP) has been discovered. At these ultra-relativistic energies the net-baryon density is approaching to zero and transition from the sQGP to hadron gas is a smooth crossover. Future physics programs are focused on the study of the sQGP properties. On the other hand, new questions are raised: What is the QCD phase structure at finite net-baryon density? Where is the QCD critical point? In the first phase of the beam energy scan program (BES-I) at RHIC, we have collected data from Au+Au collisions at the center of mass energy range from 7.7 to 39 GeV, corresponding to the baryonic chemical potential of 420 to 120 MeV, respectively. We have observed the disappearance of the suppression of leading hadrons at large momenta, break down of the quark scaling in the identified particle elliptic flow, the net-proton directed flow slope dv1/dy shows a minimum with negative sign, and a non-monotonical behavior of the net-proton correlation function (the fourth order) at the energy less than 20 GeV. All of these observations indicate that the property of the medium at high baryon density is dramatically different from that created at the RHIC top energy where the baryon density is small and partonic interactions are dominant. In this talk I will first review what we have learned in RHIC BES-I. Then I will discuss the opportunities in the future bean energy scan program in order to address key questions regarding the QCD phase structure including the illusive critical point. I will stress that adequate detector upgrades, focused at the large baryon density region, are essential for the physics program.

报告人简介：Prof. Xu Nu works at Central China Normal University and Lawrence Berkeley National Laboratory. He received his Ph.D. in State University of New York at Stony Brook. He is a senior staff scientist at Lawrence Berkeley National Laboratory, adjunct professor at University of Science and Technology of China. He also is Fellow of The Institute of Physics, UK (2004); American Physical Society Fellow, USA (2009); 1000-Plan, China (2010).

第148期“论坛”主请人联系方式：
何红建   62788895   hjhe@tsinghua.edu.cn