"Figure 12a" of "A detailed study of high-p(T) neutral pion suppression and azimuthal anisotropy in Au + Au collisions at s(NN)**(1/2) = 200-GeV."

Measurements of neutral pion $(\pi^0)$ production at midrapidity in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions as a function of transverse momentum, $p_T$, collision centrality, and angle with respect to reaction plane are presented. The data represent the final $\pi^0$ results from the PHENIX experiment for the first RHIC Au+Au run at design center-of-mass-energy. They include additional data obtained using the PHENIX Level-2 trigger with more than a factor of three increase in statistics over previously published results for $p_T$ > 6 GeV/$c$. We evaluate the suppression in the yield of high-$p_T$ $\pi^0$'s relative to point-like scaling expectations using the nuclear modification factor $R_{AA}$. We present the $p_T$ dependence of $R_{AA}$ for nine bins in collision centrality. We separately integrate $R_{AA}$ over larger $p_T$ bins to show more precisely the centrality dependence of the high-$p_T$ suppression. We then evaluate the dependence of the high-$p_T$ suppression on the emission angle $\Delta\phi$ of the pions with respect to event reaction plane for $7$ bins in collision centrality. We show that the yields of high-$p_T$ $\pi^0$'s vary strongly with $\Delta\phi$, consistent with prior measurements. We show that this variation persists in the most peripheral bin accessible in this analysis. For the peripheral bins we observe no suppression for neutral pions produced aligned with the reaction plane while the yield of $\pi^0$'s produced perpendicular to the reaction plane is suppressed by more than a factor of $~ 2$. We analyze the combined centrality and $\Delta\phi$ dependence of the $\pi^0$ suppression in different $p_T$ bins using different possible descriptions of parton energy loss dependence on jet path-length averages to determine whether a single geometric picture can explain the observed suppression pattern.

本文呈现了质心系能量√s_NN=200 GeV的金金（Au+Au）碰撞中，快度中段中性π介子（π⁰）的产额测量结果，其作为横向动量p_T、碰撞中心度以及相对于反应平面夹角的函数。该数据集为PHENIX探测器实验在相对论重离子对撞机（RHIC）首次达到设计质心系能量的金金碰撞运行中所获得的中性π介子最终测量结果。相较于此前已发表的p_T>6 GeV/c区间的测量结果，本次数据集通过使用PHENIX二级触发（Level-2 trigger）获取了额外数据，统计量提升超过3倍。我们借助核修正因子R_AA，对比类点标度预期，评估了高横向动量π⁰的产额压低效应。我们给出了9个碰撞中心度区间内R_AA随p_T的变化关系，并通过在更大的p_T区间内对R_AA进行积分，更精准地展示了高p_T产额压低效应随碰撞中心度的依赖关系。随后，我们针对7个碰撞中心度区间，分析了高p_T π⁰的产额压低效应随π介子发射角Δφ（相对于事件反应平面）的依赖关系。结果表明，高p_T π⁰的产额随Δφ存在显著变化，这与此前的测量结果一致，且该角度依赖关系在本次分析可触及的最边缘碰撞事例区间内依然存在。在边缘碰撞区间中，与反应平面同向产生的中性π介子未出现产额压低，而垂直于反应平面产生的π⁰产额则被压低约2倍以上。我们基于多种描述部分子能量损失对喷注路径长度平均值依赖关系的模型，分析了不同p_T区间内π⁰产额压低效应的中心度与Δφ联合依赖特性，以此判断单一几何图像能否解释观测到的产额压低模式。