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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. 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 this talk I will first review what we have learned in RHIC beam energy scan program (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. |