AI 中文总结
研究重离子碰撞中J/ψ介子自旋取向，基于双组分玻尔兹曼输运模型推导自旋密度矩阵元ρ₀₀，解释ALICE测量结果，给出前向和中快度区域ρ₀₀的p_T依赖性预测及趋势，阐明其自旋取向机制，推进重夸克偶素自旋动力学理解。
AI 中文摘要
我们在双组分玻尔兹曼输运模型中研究相对论重离子碰撞中J/ψ介子的自旋取向。从相对论自旋玻尔兹曼方程出发，在重夸克的非相对论近似下推导出自旋密度矩阵元ρ₀₀。为解释近期ALICE在Pb+Pb碰撞中的测量结果，将观测到的ρ₀₀描述为原初产生和聚结过程贡献的p_T依赖混合。在前向快度下，这种双组分机制很好地再现了粲夸克偶素ρ₀₀的p_T依赖性。我们还给出了中快度区域J/ψ ρ₀₀的预测，因热涡度贡献的运动学抑制呈现出不同的p_T趋势。该研究阐明了J/ψ自旋取向的潜在机制，推进了我们对强相互作用物质中重夸克偶素自旋动力学的理解。
英文摘要
We investigate the spin alignment of $J/ψ$ mesons in relativistic heavy-ion collisions within a two-component Boltzmann transport model. Starting from the relativistic spin Boltzmann equation, we derive the spin density matrix element $ρ_{00}$ under a non-relativistic approximation for heavy quarks. To interpret the recent ALICE measurements in Pb+Pb collisions, the observed $ρ_{00}$ is described as a $p_T$-dependent mixture of contributions from primordial production and the coalescence process. At forward rapidity, the $p_T$ dependence of charmonium $ρ_{00}$ is well reproduced by this two-component mechanism: at low $p_T$, charmonium production is dominated by the coalescence of partially polarized charm quarks induced by thermal vorticity; with increasing $p_T$, primordially produced charmonia become dominant, causing $ρ_{00}$ to approach $1/3$. To further test this spin alignment mechanism, we provide predictions for the $J/ψ$ $ρ_{00}$ in the mid-rapidity region, which exhibits a distinct $p_T$ trend due to the kinematic suppression of the thermal vorticity contribution. This study elucidates the underlying mechanism of $J/ψ$ spin alignment and advances our understanding of heavy quarkonium spin dynamics in strongly interacting matter.
