"fig5_bottom_left_8" 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）碰撞过程，探究了带电粒子相对于喷注轴的角分布随喷注相对于事件平面（event plane）的取向变化规律。此项差分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，其能量损失随路径长度变化的理论预期。分析过程中采用二阶事件平面，作为由碰撞冲击参数与束流方向所定义的反应平面（reaction plane）的实验估计量。在20%~50%的碰撞中心度区间内，我们采用半径参数$R=0.4$的反$k_T$（anti-$k_T$）算法，重建横动量满足$15 < p_{T, ext{jet}} <20$ GeV/$c$与$20 < p_{T, ext{jet}} <40$ GeV/$c$的带电粒子喷注，以最大化相互作用区域的初始态偏心率。相较于此前的研究方法，本研究采用反应平面拟合方法，以更高精度移除了受流体力学流效应调制的本底信号。我们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，进一步量化了事件平面依赖效应。在本研究涵盖的运动学区间内，未观测到喷注轴相对于事件平面的取向存在显著依赖，其结果处于实验误差允许范围之内。这一发现与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结果一致。