Nuclear Physics Seminar

Abstract:
The main motivation of the RHIC beam energy scan (BES) program is to study the quantum chromodynamics (QCD) phase diagram. Systematic analysis of Au+Au collisions from sNN−−−−√ = 39 GeV down to 7.7 GeV in the RHIC BES-I could help to achieve the following goals: 1) to find the QCD critical point where the first order phase transition at finite baryon chemical potential ends and to identify the phase boundary of the first order phase transition; 2) to locate the collision energy where deconfinement begins.
Strange hadrons are an excellent probe for identifying the phase boundary and onset of deconfinement. In particular, the strange quark production rate and its subsequent evolution in the hot and dense nuclear medium depend on the collision energy, the net baryon density and the system size. We will review recent STAR measurements of KS, K±, ?, Λ, Ξ, and Ω at mid-rapidity from the RHIC BES-I. We will discuss the strangeness enhancement through the ratios K/π, Λ/π, ?/π and Ξ/π, and strangeness equilibration as a function of collision energy and charged hadron multiplicity. Nuclear modification factors and baryon to meson ratios will be discussed to understand the hadron production mechanisms. Implications on partonic vs. hadronic dynamics at the RHIC BES-I energy range will be discussed. The prospects for the on-going RHIC BES-II will also be discussed.