"fig5_top_right_9" 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√s_{NN}=200 GeV的金-金（Au+Au）碰撞，开展了带电粒子相对于喷注轴的角分布研究，分析变量为喷注相对于事件平面（event plane）的方位。此项差分研究旨在验证硬散射部分子（hard-scattered parton）在穿越重离子碰撞中形成的热密介质时，其能量损失所预期的路径长度依赖性。分析过程中采用二阶事件平面，作为对由碰撞参数与束流方向共同构建的反应平面（reaction plane）的实验估算量。针对15 < p_{T,jet} < 20 GeV/c与20 < p_{T,jet} < 40 GeV/c两个横向动量区间的带电粒子喷注，本研究在20%-50%中心度区间内，采用半径参数R=0.4的反$k_T$（anti-$k_T$）算法进行喷注重建，以最大化相互作用区的初始态偏心率。本次研究采用反应平面拟合方法，相较于此前的实验手段，可更精准地去除流调制本底。研究者在喷注轴与事件平面之间的三个角区间内，提取了喷注关联带电强子分布的产额与宽度。进一步通过不同事件平面（EP）区间内的关联产额比值，对事件平面依赖性进行量化分析。在所研究的运动学区域内，未观测到带电粒子角分布与喷注轴相对于事件平面的方位存在相关性。该实验结果与ALICE合作组在√s_{NN}=2.76 TeV的铅-铅（Pb+Pb）碰撞数据中得到的类似观测结果一致。