Variable Energy Cyclotron Centre, Homi Bhabha National Institute.
Nuclear Physics Institute of the Czech Academy of Sciences.
Phys Rev Lett. 2019 Oct 4;123(14):142301. doi: 10.1103/PhysRevLett.123.142301.
Measurements of anisotropic flow coefficients (v_{n}) and their cross-correlations using two- and multiparticle cumulant methods are reported in collisions of pp at sqrt[s]=13 TeV, p-Pb at a center-of-mass energy per nucleon pair sqrt[s_{NN}]=5.02 TeV, Xe-Xe at sqrt[s_{NN}]=5.44 TeV, and Pb-Pb at sqrt[s_{NN}]=5.02 TeV recorded with the ALICE detector. The multiplicity dependence of v_{n} is studied in a very wide range from 20 to 3000 particles produced in the midrapidity region |η|<0.8 for the transverse momentum range 0.2<p_{T}<3.0 GeV/c. An ordering of the coefficients v_{2}>v_{3}>v_{4} is found in pp and p-Pb collisions, similar to that seen in large collision systems, while a weak v_{2} multiplicity dependence is observed relative to nucleus-nucleus collisions in the same multiplicity range. Using a novel subevent method, v_{2} measured with four-particle cumulants is found to be compatible with that from six-particle cumulants in pp and p-Pb collisions. The magnitude of the correlation between v_{n}^{2} and v_{m}^{2}, evaluated with the symmetric cumulants SC(m,n) is observed to be positive at all multiplicities for v_{2} and v_{4}, while for v_{2} and v_{3} it is negative and changes sign for multiplicities below 100, which may indicate a different v_{n} fluctuation pattern in this multiplicity range. The observed long-range multiparticle azimuthal correlations in high multiplicity pp and p-Pb collisions can neither be described by pythia 8 nor by impact-parameter-Glasma, music, and ultrarelativistic quantum molecular dynamics model calculations, and hence, provide new insights into the understanding of collective effects in small collision systems.
使用二粒子和多粒子关联矩方法，测量了 pp 在 sqrt[s]=13 TeV、p-Pb 在每核子对质心能量 sqrt[s_{NN}]=5.02 TeV、Xe-Xe 在 sqrt[s_{NN}]=5.44 TeV 和 Pb-Pb 在 sqrt[s_{NN}]=5.02 TeV 碰撞中的各向异性流系数（v_{n}）及其关联，并在 midrapidity 区域 |η|<0.8 内测量了横动量范围 0.2<p_{T}<3.0 GeV/c 中产生的 20 到 3000 个粒子的非常宽的多重数范围内研究了 v_{n}的多重数依赖性。在 pp 和 p-Pb 碰撞中发现 v_{2}>v_{3}>v_{4} 的系数排序与在大碰撞系统中看到的相似，而在相同多重数范围内与核-核碰撞相比，v_{2}对多重数的依赖性较弱。使用一种新的子事件方法，发现用四粒子关联矩测量的 v_{2}与 pp 和 p-Pb 碰撞中的六粒子关联矩的 v_{2}兼容。用对称关联矩 SC(m,n) 评估的 v_{n}^{2}和 v_{m}^{2}之间的相关性大小，在所有多重数下，对于 v_{2}和 v_{4}，其值为正，而对于 v_{2}和 v_{3}，其值为负，且在低于 100 的多重数下改变符号，这可能表明在这个多重数范围内 v_{n}的波动模式不同。在高多重数的 pp 和 p-Pb 碰撞中观察到的长程多粒子方位角关联既不能用 pythia 8 也不能用 impact-parameter-Glasma、music 和 ultrarelativistic quantum molecular dynamics 模型计算来描述，因此为理解小碰撞系统中的集体效应提供了新的见解。
