碰撞几何构型对相对论重离子碰撞旁观者核子的影响

Collision Geometry Effect on Free Spectator Nucleons in Relativistic Heavy-ion Collisions

在不同的核物质对称能下利用约束的Skyrme-Hartree-Fock-Bogolyubov计算得到了形变核的核子分布,基于此计算了RHIC能量下形变核碰撞产生的自由旁观者核子数及中质子产额比,并分析了中子皮和碰撞几何构型的影响。本工作发现,相比于其他碰撞构型,长椭球核的头对头碰撞和扁椭球核的腰对腰碰撞产生的自由旁观者核子数最少。旁观者中质子产额比敏感于中子皮的平均厚度,因此是对称能的良好探针,但不同碰撞几何构型所得到的产额比依赖于中子皮的极化角分布。在某些碰撞体系中,碰撞几何构型的效应大约为对称能效应的50%。由于238U和96Zr的特殊形变中子皮,相对于其他碰撞构型,旁观者中质子产额比对对称能的敏感性在头对头的238U+238U碰撞和腰对腰的96Zr+96Zr碰撞得到了增强。此研究可能开启新的研究方向,即通过筛选高能形变核碰撞的几何构型来研究形变的中子皮分布。

Based on the deformed nucleon distributions obtained from the constrained Skyrme-Hartree-FockBogolyubov calculation using different nuclear symmetry energies,we have investigated the effects of the neutron skin and the collision geometry on the yield of free spectator nucleons as well as the yield ratio of free spectator neutrons to protons in collisions of deformed nuclei at RHIC energies.We found that tip-tip(body-body)collisions with prolate(oblate)nuclei lead to fewest free spectator nucleons,compared to other collision configurations.While the ratio is sensitive to the average neutron-skin thickness of colliding nuclei,and is thus a good probe of the symmetry energy,it is affected by the polar angular distribution of the neutron skin in different collision configurations.We also found that the collision geometry effect can be as large as 50%the symmetry energy effect in some collision systems.Due to the particular deformed neutron skin in 238U and 96Zr,the symmetry energy effect on the ratio is enhanced in tip-tip 238U+238U collisions and body-body 96Zr+96Zr collisions compared to other collision configurations in the same collision system.Our study may shed light on probing deformed neutron skin by selecting desired configurations in high-energy collisions with deformed nuclei.