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Advances in High Energy Physics
Volume 2016 (2016), Article ID 9317873, 8 pages
Research Article

Impact Parameter Dependence of Ratio in Probing the Nuclear Symmetry Energy Using Heavy-Ion Collisions

1Shaanxi Key Laboratory of Surface Engineering and Remanufacturing, School of Mechanical and Material Engineering, Xi’an University, Xi’an 710065, China
2Department of Physics and Astronomy, Texas A&M University-Commerce, Commerce, TX 75429-3011, USA
3School of Electronic Engineering, Xi’an Shiyou University, Xi’an 710065, China

Received 18 August 2015; Revised 12 December 2015; Accepted 14 December 2015

Academic Editor: Frank Filthaut

Copyright © 2016 Gao-Feng Wei et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The publication of this article was funded by SCOAP3.


The impact parameter dependence of ratio is examined in heavy-ion collisions at 400 MeV/nucleon within a transport model. It is shown that the sensitivity of ratio on symmetry energy shows a transition from central to peripheral collisions; that is, the stiffer symmetry energy leads to a larger ratio in peripheral collisions while the softer symmetry energy always leads this ratio to be larger in central collisions. After checking the kinematic energy distribution of ratio, we found this transition of sensitivity of ratio to symmetry energy is mainly from less energetic pions; that is, the softer symmetry energy gets the less energetic pions to form a smaller ratio in peripheral collisions while these pions generate a larger ratio in central collisions. Undoubtedly, the softer symmetry energy can also lead more energetic pions to form a larger ratio in peripheral collisions. Nevertheless, considering that most of pions are insufficiently energetic at this beam energy, we therefore suggest the ratio as a probe of the high-density symmetry energy effective only in central at most to midcentral collisions, thereby avoiding the possible information of low-density symmetry energy carried in ratio from peripheral collisions.