While jet quenching in relativistic heavy-ion collisions has been extensively studied over decades, the polarization of quenched hadrons has rarely been discussed. It has recently been proposed that the correlations of dihadron polarization in $e^+e^-$ and $pp$ collisions provide a novel probe of the longitudinal spin transfer from hard partons to hadrons without requiring the colliding beams to be polarized. To support realistic experimental measurement of dihadron polarization with sufficient luminosity, we extend the aforementioned study to relativistic heavy-ion collisions by convoluting the vacuum fragmentation of partons with their energy loss inside the quark-gluon plasma (QGP). We find that while the correlation functions of $Λ$-$Λ$ (or $Λ$-$\barΛ$) polarization in peripheral collisions is consistent with those in $pp$ collisions, clear enhancement can be seen in central collisions. These correlation functions appear sensitive to different assumptions in the DSV parameterization of parton fragmentation functions, and therefore could place additional constraints on the spin-dependent fragmentation functions of quarks and gluons. The correlation of dihadron polarization has also been explored in ultraperipheral heavy-ion collisions, which provides a cleaner probe of fragmentation functions of quarks produced by energetic photon-photon and photon-pomeron interactions.
Diffractive vector meson photo-production in oxygen-oxygen and neon-neon ultraperipheral collisions at energies available at the CERN Large Hadron Collider
Peripheral, ultrarelativistic production of particles in heavy ion collisions
本文用等效光子近似（EPA）计算了超周边超相对论重离子碰撞中双π介子的产生截面。给出了碰撞参数、双π不变质量、单π和双π快度、π横动量和π赝快度的微分分布。$γγ\to π^+ π^-$子过程构成了$A A \to A ρ^0 (\to π^+ π^-) A$过程的背景，由碰撞核之一发射光子引发。由于$A A \to A ρ^0 A$反应的横截面非常大，所以只有一部分与$γγ$-碰撞相关的双π不变质量分布是可见的。本文给出了超周边超相对论碰撞中双散射机制下双$ρ^0$介子产生的微分分布。$γA \to ρ^0 A$的横截面根据文献计算进行参数化。考虑了$ρ^0$质量的涂抹。计算结果进行了比较，在RHIC获得的实验数据和双光子机制的贡献。与$γγ$聚变相比，双散射机制填充了更大的$ρ^0 ρ^0$不变质量和两个$ρ^0$介子之间更大的快度距离。它对$A A \to A A π^+ π^- π^+ π^-$反应有显著贡献。提出了与带电π介子有关的一些观测量。我们的计算结果进行了比较与STAR合作的结果为四个电荷的π生产。虽然四π介子系统的不变质量形状与测量的非常相似，但预测的截面仅占测量截面的20%。\end{abstract}
Analysis of $J/ψ$ and $ψ(2S)$ Charmonium Production in Ultraperipheral Lead-Lead and Proton-Lead Collisions at LHC Energies
Department of physics, Lanzhou University of Technology（兰州理工大学物理系）；Institute of Modern Physics, Fudan University（复旦大学现代物理研究所）；Lanzhou Center for Theoretical Physics, Key Laboratory of Theoretical Physics of Gansu Province, and Key Laboratory of Quantum Theory and Applications of MoE, Lanzhou University（兰州大学理论物理中心、甘肃省理论物理重点实验室和教育部量子理论与应用重点实验室）
