基于双粒子方位角关联方法研究费米能区重离子碰撞中横向流的入射能量依赖关系

Study of Transverse Flow Dependence on Incident Energy in Heavy-ion Collisions near the Fermi Energy Based on Two-particle Azimuthal Correlation Approach

基于双粒子方位角关联(2pAC)方法开展了费米能区^(64)Zn轰击^(58)Ni靶的重离子碰撞中横向流入射能量依赖的实验研究。利用考虑了单个事件中参考粒子对剩余体系反冲修正的改进的2pAC方法和已有的2pAC方法分别抽取了26,35和47 MeV/u能量下^(64)Zn+^(58)Ni半中心碰撞的相对横向流强度,发现横向流的强度随入射能量增加而减弱的趋势与抽取横向流过程中是否考虑反冲修正无关,但考虑反冲修正时得到的横向流相对强度对比未考虑反冲修正时显著减小。通过线性拟合得到的相对横向流强度-入射能量关系,进一步获得了^(64)Zn+^(58)Ni半中心碰撞的平衡能分别为(110.1±5.8)MeV/u(改进的2pAC方法)和(128.0±5.6)MeV/u(已有的2pAC方法)。对比以往基于常规反应平面重建方法抽取得到的结果发现,基于改进的2pAC方法得到的结果与以往基于常规方法测得的平衡能-碰撞参数关系符合很好;相反,基于已有2pAC方法得到的结果被显著高估。对比结果证明了在利用2pAC方法抽取横向流强度的过程中考虑反冲修正的必要性,以及在平衡能研究中采用改进的2pAC方法与依赖于反应平面重建的常规方法的等价性。

In this article,the incident energy dependence of transverse flow from the collisions of ^(64)Zn+^(58)Ni near the Fermi energy is investigated experimentally based on a two-particle azimuthal correlation(2pAC)approach.The transverse flow values from the mid-peripheral collisions at the incident energies of 26,35 and 47 MeV/u are extracted using the 2pAC approaches with and without the specific consideration of the recoil effect from the emitted particle of interest to the residue in an event-by-event basis,respectively.The flow values extracted from both approaches show consistently increasing trend as a function of incident energy.In contrast,the flow values for the three energies show different in magnitude,that those from the improved 2pAC approach with the consideration of the recoil effect are significantly reduced.The balance energy of the mid-peripheral ^(64)Zn+^(58)Ni collisions is further investigated using linear fit for the obtained transverse flow versus incident energy,and two balance energy values are obtained to be(110.1±5.8)MeV/u for the improved 2pAC approach and(128.0±5.6)MeV/u for the original 2pAC approach,respectively.These two values are compared with those previously measured based on the conventional flow extraction approach involving the reaction plane reconstruction process.It is found that the balance energy from the improved 2pAC approach,rather than that from the original 2pAC approach,follows well the relation of balance energy versus impact parameter from the conventional approach.This comparison suggests the necessity for considering the recoil effect correction in the flow extraction using the 2pAC approach,and the equivalence between the improved 2pAC approach and the conventional flow extraction approach involving the reaction plane reconstruction process in the investigation on the balance energy.