$p$ +Pb碰撞的微扰和非微扰QCD研究
Investigations of $p$+Pb Collisions at Perturbative and Non-Perturbative QCD Scales
摘要：
高能核碰撞在很宽的能量尺度范围内表现出各种有趣的现象。这些现象中的许多都与一种热而致密的退禁闭夸克和胶子态的形成有关，这种状态被称为夸克-胶子等离子体（QGP）。其中最主要的是通过低$p_\mathrm{T}$末态强子$v_\mathrm{n}$的方位角各向异性系数测量的QGP的近无粘流体动力学膨胀，以及高$p_\mathrm{T}$色荷穿过QGP时的能量损失，这被观察为强相互作用末态物体如喷流的淬灭。在RHIC和LHC的Au+Au和Pb+Pb碰撞中观察到的这些现象为QGP的形成提供了令人信服的证据。小碰撞系统，如$p$ +Pb，也显示出通过各向异性流的观察，QGP的创建液滴的证据;然而，这些系统没有显示出在大碰撞系统中观察到的能量损失的迹象。因此，小系统是一个理想的场所，探讨之间的关系，高-和低- $p_\mathrm{T}$ QGP现象。此外，与A+A碰撞相比，$p$ +Pb的低环境能量允许精确确定微扰过程速率，其可用于理解核子部分子密度的核修改。本论文研究了在大型强子对撞机上用ATLAS探测器收集的$p$ +Pb数据。的截面和核修改因子的提示，孤立的光子测量和比较从微扰QCD计算和模型的初始状态能量损失的预测。此外，带电强子方位各向异性系数，测量通过两个粒子的关联作为粒子$p_\mathrm{T}$和事件中心性的函数。结果显示了最小偏差事件和由于高$p_\mathrm{T}$喷流的存在而选择的事件。
英文摘要：
High energy nuclear collisions manifest a variety of interesting phenomena over a broad range of energy scales. Many of these phenomena are related to the formation of a hot and dense state of deconfined quarks and gluons known as the quark gluon plasma (QGP). Chief among these are the observed near inviscid hydrodynamic expansion of the QGP, as measured through azimuthal anisotropy coefficients of low-$p_\mathrm{T}$ final state hadrons $v_\mathrm{n}$, and the loss of energy of high-$p_\mathrm{T}$ color charges as they traverse the QGP which is observed as a quenching of strongly-interacting final state objects like jets. Observations of these phenomena in Au+Au and Pb+Pb collisions at RHIC and the LHC provide compelling evidence of QGP formation. Small collision systems, like $p$+Pb, also show evidence for the creation droplets of QGP through the observation of anisotropic flow; however, these systems show no signs of the energy loss observed in large collision systems. Thus, small systems are an ideal venue to explore the relationship between high- and low-$p_\mathrm{T}$ QGP phenomena. Furthermore, the low ambient energy of $p$+Pb compared to A+A collisions allow for the precise determination of perturbative process rates which can be used to understand the nuclear modification of nucleon parton densities. This dissertation explores $p$+Pb data collected with the ATLAS detector at the LHC. The cross section and nuclear modification factor for prompt, isolated photons are measured and compared to predictions from perturbative QCD calculations and a model of initial state energy loss. Additionally, the charged hadron azimuthal anisotropy coefficients, are measured via two-particle correlations as a function of particle $p_\mathrm{T}$ and event centrality. Results are shown from minimum bias events and events selected because of the presence of a high-$p_\mathrm{T}$ jet.
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