Measurement of multi-particle azimuthal correlations with the subevent cumulant method in $pp$ and $p$+Pb collisions with the ATLAS detector at the LHC
A detailed study of multi-particle azimuthal correlations is presented using $pp$ data at $\sqrt{s}=5.02$ and 13 TeV, and $p$+Pb data at $\sqrt{s_{\rm{NN}}}=5.02$ TeV, recorded with the ATLAS detector at the LHC. The azimuthal correlations are probed using four-particle cumulants $c_{n}\{4\}$ and flow coefficients $v_n\{4\}=(-c_{n}\{4\})^{1/4}$ for $n=2$ and 3, with the goal of extracting long-range multi-particle azimuthal correlation signals and suppressing the short-range correlations. The values of $c_{n}\{4\}$ are obtained as a function of the average number of charged particles per event, $\left\langle N_{\rm{ch}} \right\rangle$, using the recently proposed two-subevent and three-subevent cumulant methods, and compared with results obtained with the standard cumulant method. The three-subevent method is found to be least sensitive to short-range correlations, which originate mostly from jets with a positive contribution to $c_{n}\{4\}$. The three-subevent method gives a negative $c_{2}\{4\}$, and therefore a well-defined $v_2\{4\}$, nearly independent of $\left\langle N_{\rm{ch}} \right\rangle$, which provides direct evidence that the long-range multi-particle azimuthal correlations persist to events with low multiplicity. Furthermore, $v_2\{4\}$ is found to be smaller than the $v_2\{2\}$ measured using the two-particle correlation method, as expected for long-range collective behavior. Finally, the measured values of $v_2\{4\}$ and $v_2\{2\}$ are used to estimate the number of sources relevant for the initial eccentricity in the collision geometry.
Correlations of azimuthal anisotropy Fourier harmonics with subevent cumulants in pPb collisions at $\sqrt{s_\mathrm{NN}} =$ 8.16 TeV
利用子事件四粒子累积量技术，提取了8.16 TeV pPb碰撞数据中方位各向异性傅立叶系数（$v_n$）的逐事件关联.四个带电粒子的每个组合选自CMS跟踪器的伪快度范围从$-$ 2.4到2.4的两个、三个或四个不同的子事件区域，并且横向动量在0.3和3.0 GeV之间。使用子事件累积量技术，测量不同阶数的$v_n$之间的相关性作为粒子多重性的函数，并与没有子事件的标准累积量方法进行比较。在高多重性下，$v_2$和$v_3$系数表现出线性关系;使用各种方法一致地观察到这种行为。的$v_2$和$v_4$相关强度被发现依赖于在计算中使用的子事件的数量。当事件多重数减少时，由于非集体关联或少粒子关联的贡献不同，不同的子事件方法的结果会产生分歧。与四子事件方法提取的相关性表现出单调减少的趋势，向最低的多重性区域（约20个带电轨道）调查。这些研究结果扩展了以前的研究，以显着降低事件的多重性范围，并建立了证据，在小系统碰撞的远程集体多粒子相关性的发病。
Correlated long-range mixed-harmonic fluctuations measured in $pp$, $p$+Pb and low-multiplicity Pb+Pb collisions with the ATLAS detector
在13 TeV $pp$、5.02 TeV $p$ +Pb和2.76 TeV外围Pb+Pb碰撞中，用ATLAS探测器测量了两个流谐波$v_n$和$v_m$通过三粒子和四粒子累积量的关联.目标是了解这些碰撞系统中长程集体现象的多粒子性质。在标准累积量方法中存在的大的非流动背景，从双喷生产抑制使用子事件累积量的方法，包括两个，三个和四个子事件分离的伪快度。结果表明，在所有碰撞体系和整个多重数范围内，$v_2$和$v_3$之间呈负相关，$v_2$和$v_4$之间呈正相关。然而，关联的大小强烈地依赖于事件的多重性，选择的横向动量范围和碰撞系统。的相对相关强度，通过归一化的累积量与$\langle v_n^2\rangle$从两个粒子的相关分析，是类似的三个碰撞系统，弱依赖于事件的多重性和横向动量。这些结果为$pp$、$p$ +Pb和外围Pb+Pb碰撞中类似的长程多粒子集体提供了有力的证据。
Azimuthal anisotropies of charged particles with high transverse momentum in Pb+Pb collisions at $\sqrt{s_{_\text{NN}}} = 5.02$ TeV with the ATLAS detector
Measurement of the azimuthal anisotropy of charged particles in $\sqrt{s_{\mathrm{NN}}}=5.36$ TeV $^{16}$O$+^{16}$O and $^{20}$Ne$+^{20}$Ne collisions with the ATLAS detector
EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN)（欧洲核子研究中心）
Measurements of azimuthal anisotropies at forward and backward rapidity with muons in high-multiplicity p-Pb collisions at $\sqrt{s_{\rm NN}} = 8.16$ TeV
ALICE 在 8.16 TeV 高多重数 p-Pb 碰撞中用两粒子累积量和关联法测量前、后向μ子 v_2，发现显著正各向异性，为重味集体行为理论提供新约束。
Correlations between flow and transverse momentum in Xe+Xe and Pb+Pb collisions at the LHC with the ATLAS detector: a probe of the heavy-ion initial state and nuclear deformation
DAB-MOD sensitivity study of heavy flavor $R_{AA}$ and azimuthal anisotropies based on beam energy, initial conditions, hadronization, and suppression mechanisms
Energy and system-size dependence of two- and four-particle $v_2$ measurements in heavy-ion collisions at RHIC and their implications on flow fluctuations and nonflow
