The nuclear symmetry energy varying with density is a key input to understand the isospin dynamics in heavy ion collisions (HIC) as well as the evolution properties of dense stellar objects. We study the isospin transport in HIC to seek an experimental constraint on the density dependence of the symmetry energy. Some recent results will be presented in this talk. 1) An isospin dependent hierarchy of particle emission is observed, suggesting that the relaxation of isospin degree of freedom in HIC may not be so fast as what we have learnt from existing experience. 2) The angular dependence of the neutron richness of the produced light charged particles is measured, allowing us to constrain stringently the nuclear symmetry energy below saturation density. 3) The isovector re-orientation effect of deuteron scattering off a heavy target is demonstrated to be a clean and sensitive probe of the symmetry energy at sub-saturation densities.

Bio: Zhigang Xiao graduated from Beijing Normal University in 1995 with bachelor degree in physics. He obtained his doctoral degree from the Institute of Modern Physics, Chinese Academy of Sciences in 2001. He worked in GSI and Heidelberg University with the FOPI collaboration before joining the faculty of Department of Physics, Tsinghua University as a tenure-track assistant professor in 2007. He was promoted to full professorship with tenure in 2017. He published more than 100 papers in total and received 5000+ citations on google scholar.