Faculty Compensated Leave Report

By Bin Zhang

Department of Chemistry and Physics

I spent the fall 2006 semester on compensated leave studying relativistic heavy ion collisions. My main research topic was the transport equation of state from the AMPT (A Multi-Phase Transport) model. During the informal discussions at the National Institute for Nuclear Theory, I learned that this problem is important in clarifying a few problems. One is related to the HBT (Hanbury-Brown-Twiss) interferometry. Hydrodynamic simulations have difficulty of giving perfect description of the HBT radii in spite of the spectacular success in describing other experimental observables. One parameterization of space-time evolution by Renk can give good description. However, instead of having local thermal equilibrium, this model has longitudinal pressure larger than the transverse pressure. The AMPT model can also give a reasonable description of the HBT radii. It is interesting to know how different pressures compare in the AMPT model. Another problem is related to the generation of elliptic flow. Saturation model initial conditions do not have thermal equilibration and initial longitudinal pressure is smaller than the transverse one. Current practice in using the saturation initial conditions is to assume local thermal equilibrium at an initial time. Whether different longitudinal pressure and transverse pressure can lead naturally to good description of the elliptic flow data needs to be studied. Some preliminary results on the transport equation of state were obtained. Detailed study is being carried out and can lead to an improved understanding of the above problems.

I also worked on improving the transport simulations with Dr. Hai Jiang and Dr. Hung-Chi Su at Arkansas State University. Our paper “An empirical study on many-particle collision algorithms” was accepted for publication in the Proceedings of the 22nd International Conference of Computers and Their Applications. Another paper “Toward optimizing particle-simulation systems” was submitted for publication in the Proceedings of the International Conference on Computational Science 2007.

 In addition to working on research projects, I participated in a few conferences and visited a few institutions. In August, I attended the 7th workshop on the DOE Advanced CompuTational Software (ACTS) collection the Lawrence Berkeley Lab and visited the Nuclear Theory Group at the Lawrence Berkeley Lab. I presented a “Heavy Ion Tea” series seminar titled “J/Ψ and collective flow at RHIC”. We had good discussion on heavy quark production, high transverse momentum particle production, and the perturbative transport simulation method.

 I presented the work by myself and collaborators in a talk titled “Thermalization within a kinetic approach” in September at the “Non-equilibrium Quark-Gluon Plasma” workshop at the National Institute for Nuclear Theory at University of Washington in Seattle. The workshop topics included hydrodynamics and transport models, plasma instabilities, super-symmetric Yang-Mills theories, and perturbative Quantum Chromodynamics. I presented another talk “J/Ψ production from charm coalescence” in October in the heavy flavor production session of the INT06-3 program “From RHIC to LHC: Achievements and Opportunities” and had good discussions with participants on various topics related to heavy flavor production.

I visited the China Institute for Atomic Energy in November and gave a seminar titled “Recent Progress from the AMPT model”. I also gave a poster presentation titled “J/Ψ production from charm coalescence in relativistic heavy ion collisions” at the 19^th international conference on ultra-relativistic nucleus-nucleus collisions (Quark Matter 2006) in Shanghai, China, and an oral presentation titled “Charm transport in relativistic heavy ion collisions” at the “Selected topics on heavy flavor production in high-energy collisions” workshop held in Tsinghua University in Beijing, China.

 These activities were supported by the National Science Foundation grant PHY-0554930. Additional supports were provided by the Lawrence Berkeley Lab, the National Institute for Nuclear Theory (INT) at the University of Washington, Tsinghua University, the National Natural Science Foundation of China, China Center for Advanced Science and Technology.