"fig6_bottom_right_0" of "Jet-hadron correlations with respect to the event plane in $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV Au+Au collisions in STAR"

Angular distributions of charged particles relative to jet axes are studied in $\sqrt{s_{NN}} = 200$ GeV Au+Au collisions as a function of the jet orientation with respect to the event plane. This differential study tests the expected path-length dependence of energy loss experienced by a hard-scattered parton as it traverses the hot and dense medium formed in heavy-ion collisions. A second-order event plane is used in the analysis as an experimental estimate of the reaction plane formed by the collision impact parameter and the beam direction. Charged-particle jets with $15 < p_{T, jet} <$ 20 and $20 < p_{T, jet} <$ 40 GeV\c were reconstructed with the anti-$k_T$ algorithm with radius parameter setting of $R=0.4$ in the 20-50% centrality bin to maximize the initial-state eccentricity of the interaction region. The reaction plane fit method is implemented to remove the flow-modulated background with better precision than prior methods. Yields and widths of jet-associated charged-hadron distributions are extracted in three angular bins between the jet axis and the event plane. The event-plane (EP) dependence is further quantified by ratios of the associated yields in different EP bins. No dependence on orientation of the jet axis with respect to the event plane is seen within the uncertainties in the kinematic regime studied. This finding is consistent with a similar experimental observation by ALICE in $\sqrt{s_{NN}} = 2.76$ TeV Pb+Pb collision data.

本研究针对核子-核子质心系能量$sqrt{s_{NN}}=200$ GeV的金金（Au+Au）碰撞中，带电粒子相对于喷注轴的角分布展开分析，并将其作为喷注相对于事件平面（event plane）取向的函数进行系统性研究。这项微分测量研究旨在验证硬散射部分子穿越重离子碰撞中形成的高温致密介质时，其能量损失所预期的路径长度依赖特性。分析过程中采用二阶事件平面，作为对由碰撞冲击参数与束流方向共同定义的反应平面（reaction plane）的实验估算。本分析选取20%-50%中心度区间以最大化相互作用区的初始态偏心率，并利用半径参数$R=0.4$的反$k_T$（anti-$k_T$）算法，重建横向动量$p_{T, mathrm{jet}}$分别处于$15 < p_{T, mathrm{jet}} < 20$ GeV/$c$与$20 < p_{T, mathrm{jet}} < 40$ GeV/$c$范围内的带电粒子喷注。本研究采用反应平面拟合方法，相较于此前的实验手段，能够以更高精度移除受流体力学流效应调制的背景信号。研究人员在喷注轴与事件平面之间的三个角度区间内，提取了喷注关联带电强子分布的产额与宽度。通过不同事件平面（EP）区间内的关联产额比值，可进一步量化分布对事件平面的依赖关系。在本研究考察的运动学区域内，未在实验不确定度范围内观测到喷注轴相对于事件平面的取向依赖效应。该观测结果与ALICE合作组在$sqrt{s_{NN}}=2.76$ TeV的铅铅（Pb+Pb）碰撞数据中得到的类似实验观测一致。