"Figure 3-3" of "Creating small circular, elliptical, and triangular droplets of quark-gluon plasma"

BNL-RHIC. The experimental study of the collisions of heavy nuclei at relativistic energies has established the properties of the quark-gluon plasma (QGP), a state of hot, dense nuclear matter in which quarks and gluons are not bound into hadrons. In this state, matter behaves as a nearly inviscid fluid that efficiently translates initial spatial anisotropies into correlated momentum anisotropies among the produced particles, producing a common velocity field pattern known as collective flow. In recent years, comparable momentum anisotropies have been measured in small-system proton-proton (p+p) and proton-nucleus (p+A) collisions, despite expectations that the volume and lifetime of the medium produced would be too small to form a QGP. Here, we report on the observation of elliptic and triangular flow patterns of charged particles produced in proton-gold (p+Au), deuteron-gold (d+Au), and helium-gold (3He+Au) collisions at a nucleon-nucleon center-of-mass energy 200 GeV. The unique combination of three distinct initial geometries and two flow patterns provides unprecedented model discrimination. Hydrodynamical models, which include the formation of a short-lived QGP droplet, provide a simultaneous description of these measurements.

BNL-RHIC。在相对论能区开展的重离子碰撞实验研究，已确立了夸克胶子等离子体（quark-gluon plasma, QGP）的相关性质——这是一种高温致密的核物质状态，其中夸克与胶子不再被束缚于强子之中。在该物态下，物质表现为近乎无粘滞性的流体，可将初始空间各向异性高效转化为末态产生粒子间的关联动量各向异性，进而形成被称为集体流的通用速度场模式。近年来，尽管此前预期所产生介质的体积与寿命过小而无法形成QGP，但人们已在小系统的质子-质子（p+p）与质子-原子核（p+A）碰撞中测量到了类似的动量各向异性信号。本文报道了在核子-核子质心系能量200 GeV下，质子-金核（p+Au）、氘核-金核（d+Au）与氦-3-金核（³He+Au）碰撞中产生的带电粒子的椭圆流与三角流模式的观测结果。三种独特初始几何构型与两种流模式的独特组合，为模型甄别提供了前所未有的契机。包含短寿命QGP液滴形成过程的流体动力学模型，可同时对上述测量结果给出自洽描述。