"fig5_top_right_6" 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√s_NN=200 GeV的金金（Au+Au）碰撞过程，开展了带电粒子相对于喷注轴（jet axis）的角分布随喷注相对于事件平面（event plane）取向的依赖关系研究。此项差分分析旨在检验硬散射部分子（hard-scattered parton）穿越重离子碰撞（heavy-ion collisions）中形成的热密介质（hot and dense medium）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，作为由碰撞参数（collision impact parameter）与束流方向（beam direction）所构成的反应平面（reaction plane）的实验估算量。本工作在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，重建横动量范围为15 < p_{T,jet} < 20 GeV/c 与 20 < p_{T,jet} < 40 GeV/c的带电粒子喷注（charged-particle jets），以最大化相互作用区域的初始态偏心率（initial-state eccentricity）。为相较于此前方法实现更高精度的流调制背景（flow-modulated background）扣除，本研究采用了反应平面拟合方法。研究在喷注轴与事件平面之间的三个角度区间（angular bins）内，提取了喷注关联带电强子分布（jet-associated charged-hadron distributions）的产额与宽度。进一步通过不同事件平面区间内的关联产额之比，量化了事件平面（EP）的依赖效应。在本研究覆盖的运动学区域（kinematic regime）内，未观测到喷注轴相对于事件平面的取向存在显著依赖关系，该结果与ALICE实验在√s_NN=2.76 TeV铅铅（Pb+Pb）碰撞数据中得到的类似实验观测结果一致。

搜集汇总

背景与挑战

背景概述

该数据集是 STAR 合作组在 √sNN = 200 GeV 的 Au+Au 碰撞中，研究喷注-强子关联与事件平面关系的实验数据的一部分，具体表格 'fig5_top_right_6' 测量了 20-50% 中心度碰撞中 15-20 GeV/c 喷注的远侧关联带电强子产额（pT,assoc 在 0.0-10.0 GeV/c 范围内），用于分析喷注方向相对于事件平面的依赖性，以探索部分子在热密介质中的能量损失机制。数据表明在此运动学范围内未观察到显著的事件平面依赖性，与 ALICE 在更高能量下的实验结果一致。