AI 中文总结
本文首次测量了相对论重离子碰撞中光子诱导的 $J/ψ$ 相对于事件平面的衰变角分布，观测到负的二阶调制，证明 $J/ψ$ 极化与碰撞几何相关，可作为初始碰撞几何横向取向的直接探针。
AI 中文摘要
在相对论重离子碰撞中，准实光子的线性极化可以将光子诱导的矢量介子的自旋方向与碰撞几何关联起来。为了探索这种敏感性，我们首次测量了在具有强子重叠的重离子碰撞中，光子诱导的 $J/ψ$ 相对于事件平面的衰变角分布。该分析使用了STAR实验记录的质心能量为 $\sqrt{s_{\mathrm{NN}}}=200$ GeV 的 Ru+Ru 和 Zr+Zr 碰撞数据。在修正了有限的事件平面分辨率并扣除残余强子贡献后，对于 $|y^{ee}|<0.8$、$p_{\mathrm T}^{ee}<0.2~\mathrm{GeV}/c$ 和 30--80% 中心度，我们提取出负的二阶调制 $A_2^{\rm phot} = -0.39 \pm 0.11~(\mathrm{stat.}) \pm 0.04~(\mathrm{sys.})$。该调制提供了 $J/ψ$ 极化与事件平面相关的证据，正如线性极化光子所预期的那样。观测到的调制确立了极化 $J/ψ$ 光致产生作为初始碰撞几何横向取向的直接探针。
英文摘要
In relativistic heavy-ion collisions, the linear polarization of quasi-real photons can correlate the spin orientation of photon-induced vector mesons with the collision geometry. To explore this sensitivity, we present the first measurement of the decay angular distribution of photon-induced $J/ψ$ with respect to the event plane in heavy-ion collisions with hadronic overlap. The analysis uses Ru+Ru and Zr+Zr collisions at a nucleon--nucleon center-of-mass energy of $\sqrt{s_{\mathrm{NN}}}=200$ GeV recorded by STAR. After correcting for the finite event-plane resolution and subtracting the residual hadronic contribution, we extract a negative second-order modulation, $A_2^{\rm phot} = -0.39 \pm 0.11~(\mathrm{stat.}) \pm 0.04~(\mathrm{sys.})$, for $|y^{ee}|<0.8$, $p_{\mathrm T}^{ee}<0.2~\mathrm{GeV}/c$, and 30--80% centrality. This modulation provides evidence that the $J/ψ$ polarization is correlated with the event plane, as expected for linearly polarized photons. The observed modulation establishes polarized $J/ψ$ photoproduction as a direct probe of the transverse orientation of the initial collision geometry.
Comments7 pages, 3 figures
