利用超相对论量子分子动力学模型研究交变梯度同步加速器能区Au+Au碰撞中的核阻止效应

Study of nuclear stopping in Au+Au collisions at alternating gradient synchrotron energies by the ultra-relativistic quantum molecular dynamic model

运用修正的超相对论量子分子动力学模型研究了交变梯度同步加速器(AGS)能区Au+Au碰撞中的核阻止效应.该模型考虑了形成和"预形成"粒子的平均场势、核子-核子弹性散射反应截面的介质修正和碎块形成的判断条件.研究发现:在AGS能区,核阻止效应受到形成和"预形成"粒子的平均场势和核子-核子弹性散射反应截面介质修正的影响;在中心快度区自由质子的产额偏大,考虑新的碎块形成判断条件后,此模型的理论计算结果与自由质子的实验结果符合得很好.

Nuclear stopping in Au＋Au collisions at alternating gradient synchrotron energies is studied in the framework of the modified ultra-relativistic quantum molecular dynamics transport model, in which mean field potentials of both formed and＂preformed＂hadrons （from string fragmentation）, medium-modified nucleon-nucleon elastic cross sections, and cluster recognition criteria are considered. It is found that nuclear stopping is influenced by both the mean field potentials of formed and＂preformed＂hadrons and the medium modification of nucleon-nucleon elastic cross section. The free proton number is higher than that from the experimental rapidity distribution in the central region of rapidity distribution, which can be understood by considering the new criteria of judging fragments.