-
非对心的相对论重离子碰撞中, 不参与碰撞的核子会对参与碰撞的核子产生纵向拖拽, 形成一个相对于纵向倾斜的夸克胶子等离子体(QGP)火球. 同时, 对撞的原子核可将巨大的轨道角动量沉积于QGP中, 使其中的部分子沿系统总角动量方向发生自旋极化. 在光学 Glauber模型基础上, 本文构建了倾斜的三维QGP初态条件, 并结合3+1维黏滞流体力学模型CLVisc, 研究了重离子碰撞的末态带电粒子的直接流和
$ \Lambda/\bar{\Lambda} $ 超子的整体极化. 计算表明, 倾斜的初态条件与流体力学模型的结合能够较好地描述RHIC-STAR实验上观测到的直接流与超子整体自旋极化的数据. 这为人们利用这些观测量进一步约束重离子碰撞产生的核物质的初始几何与运动学状态提供了理论依据.-
关键词:
- 相对论重离子碰撞 /
- 夸克胶子等离子体 /
- 直接流 /
- $ \Lambda/\bar{\Lambda} $ 超子整体自旋极化
In non-central relativistic heavy-ion collisions, the non-colliding nucleons drag the colliding nucleons along the longitudinal direction asymmetrically, producing a longitudinally tilted quark-gluon plasma (QGP) fireball. Meanwhile, these colliding nuclei deposit a huge initial orbital angular momentum into the system, leading to the polarization of partons inside the QGP along the direction of the total angular momentum. Based on the optical Glauber model, we develop a 3-dimensional initial condition of the tilted QGP. By combining it with the (3+1)-dimensional viscous hydrodynamic model CLVisc, we investigate the directed flow of charged hadrons and the global polarization of$ \Lambda/\bar{\Lambda} $ hyperons in heavy-ion collisions. Our calculation indicates that the combination of a tilted initial condition of the QGP and the hydrodynamic model can provide a satisfactory description of the directed flow and global polarization observed at RHIC-STAR. This offers a theoretical baseline for using these observables to further constrain the initial geometry and kinematic properties of the nuclear matter created in heavy-ion collisions.-
Keywords:
- relativistic heavy ion collision /
- quark-gluon plasma /
- directed flow /
- $ \Lambda/\bar{\Lambda} $ global polarization
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图 3 末态带电强子在200 AGeV Au+Au碰撞不同中心度的赝快度分布
$ {\rm{d}}N_{{\rm{ch}}}/{\rm{d}}\eta $ . 实线为理论计算结果, 实心圆点为 RHIC-PHOBOS 的测量结果[40]Fig. 3. Pseudorapidity distribution
$ {\rm{d}}N_{{\rm{ch}}}/{\rm{d}}\eta $ of charged light hadrons in Au+Au collisions at$ \sqrt{s_{\rm{NN}}} = 200 $ GeV, compared between the CLVisc hydrodynamic calculation and the PHOBOS data[40]图 4 200 AGeV Au+Au 碰撞不同中心度的直接流
$ v_{1} $ . 左图为带电粒子直接流对赝快度的依赖, 右图为质子及反质子直接流对快度的依赖. 实验结果取自STAR实验组[43,44]Fig. 4. Directed flow
$ v_{1} $ of charged hadrons (left) and protons and anti-protons (right) in Au+Au collisions at$ \sqrt{s_{\rm{NN}}} = 200 $ GeV, compared between the CLVisc hydrodynamic calculation and the STAR data[43,44]图 5 200 AGeV Au+Au碰撞在不同中心度的超子整体自旋极化
$ P^y $ . 左图为Λ超子的四种自旋极化(thermal, shear, accT, chemical)随碰撞中心度的依赖. 右图为Λ和$ \overline{\Lambda} $ 超子的四种自旋极化之和(total = thermal + shear + accT + chemical)随中心度的依赖. 实验数取自RHIC-STAR[25]. 需要注意的是, 根据最新的超子衰变参数$ \alpha_{\Lambda} $ , STAR合作组采集到的数据点被缩放了 0.877倍Fig. 5. Global polarization
$ P^y $ of Λ and$ \bar{\Lambda} $ as a function of centrality in Au+Au collisions at$ \sqrt{s_{\rm{NN}}}=200 $ GeV, compared between the CLVisc hydrodynamic calculation and the STAR data [25]图 6 在200 AGe Au+Au碰撞中心度20%—60% 超子整体自旋极化
$ P^y $ 对横动量$ p_{\rm{T}} $ 的依赖关系. 左图为 Λ超子的四种自旋极化随横动量$ p_{\rm{T}} $ 的依赖. 右图为Λ和$ \overline{\Lambda} $ 超子四种贡献之和的整体自旋极化随横动量$ p_T $ 的依赖. 实验数据取自RHIC-STAR[25]Fig. 6. Global polarization
$ P^y $ of Λ and$ \bar{\Lambda} $ as a function of transverse momentum$ p_{\rm{T}} $ in 20%–60% Au+Au collisions at$ \sqrt{s_{\rm{NN}}}=200 $ GeV, compared between the CLVisc hydrodynamic calculation and the STAR data[25]图 7 200 AGeV Au+Au碰撞在中心度为20%–60%的超子整体自旋极化率
$ P^y $ 随赝快度$ \eta $ 的分布. 左图为Λ超子的四种自旋极化随赝快度$ \eta $ 的分布. 右图为Λ超子和$ \overline{\Lambda} $ 超子四种贡献之和的整体自旋极化率随赝快度的分布. 实验数据来自RHIC-STAR[25]Fig. 7. Global polarization
$ P^y $ of Λ and$ \bar{\Lambda} $ as a function of pseudo-rapidity in Au+Au collisions at$ \sqrt{s_{\rm{NN}}}=200 $ GeV, compared between the CLVisc hydrodynamic calculation and the STAR data[25] -
[1] Bass S A, Gyulassy M, Stoecker H, Greiner W 1999 J. Phys. G 25 R1
Google Scholar
[2] Rischke D H, Pürsün Y, Maruhn J A, Stoecker H, Greiner W 1995 Acta Phys. Hung. A 1 309
Google Scholar
[3] Bozek P 2022 Phys. Rev. C 106 L061901
Google Scholar
[4] Bozek P 2012 Phys. Rev. C 85 034901
Google Scholar
[5] Jiang Z F, Cao S S, Wu X Y, Yang C B, Zhang B W 2022 Phys. Rev. C 105 034901
Google Scholar
[6] Jiang Z F, Yang C B, Peng Q 2021 Phys. Rev. C 104 064903
Google Scholar
[7] Shen C, Alzhrani S 2020 Phys. Rev. C 102 014909
Google Scholar
[8] Ryu S, Jupic V, Shen C 2021 Phys. Rev. C 104 054908
Google Scholar
[9] Wang H, Chen J H 2022 Nucl. Sci. Tech. 33 15
Google Scholar
[10] 高建华, 黄旭光, 梁作堂, 王群, 王新年 2023 物理学报 72 072501
Gao J H, Huang X G, Liang Z T, Wang Q, Wang X N 2023 Acta Phys. Sin. 72 072501 (in Chinese)
[11] Liang Z T, Wang X N 2005 Phys. Rev. Lett. 94 102301
Google Scholar
[12] Liang Z T, Wang X N 2005 Phys. Lett. B 629 20
Google Scholar
[13] 孙旭, 周晨升, 陈金辉, 陈震宇, 马余刚, 唐爱洪, 徐庆华 2023 物理学报 72 072401
Sun X, Zhou C S, Chen J H, Chen Z Y, Ma Y G, Tang A H, Xu Q H 2023 Acta Phys. Sin. 72 072401 (in Chinese)
[14] 浦实, 黄旭光 2023 物理学报 72 071202
Pu S, Huang X G 2023 Acta Phys. Sin. 72 071202 (in Chinese)
[15] 尹伊 2023 物理学报 Accepted
Yin Y 2023 Acta Phys. Sin. this volume Accepted (in Chinese)
[16] Huang X G, Huovinen P, Wang X N 2011 Phys. Rev. C 84 054910
Google Scholar
[17] Li X W, Jiang Z F, Cao S S, Deng J 2023 Eur. Phys. J. C 83 96
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
[29] 高建华, 盛欣力, 王群, 庄鹏飞 2023 物理学报 72 072501
Gao J H, Sheng X L, Wang Q, Zhuang P F 2023 Acta Phys. Sin. 72 072501
[30] 盛欣力, 梁作堂, 王群 2023 物理学报 72 072502
Sheng X L, Liang Z T, Wang Q 2023 Acta Phys. Sin. 72 072502
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
[41] 赵新丽, 马国亮, 马余刚 2023 物理学报 Accepted
Zhao X L, Ma G L, Ma Y G 2023 Acta Phys. Sin. Accepted (in Chinese)
[42] Lan S W, Shi S S 2022 Nucl. Sci. Tech. 33 21
[43] STAR Collaboration, Abelev B I, et al. 2008 Phys. Rev. Lett. 101 252301
Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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[52] Fu B C, Liu S Y F, Pang L G, Song H C, Yin Y 2021 Phys. Rev. Lett. 127 142301
Google Scholar
[53] Fu B C, Pang L G, Song H C, Yin Y 2022 arXiv: 2201.12970.
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