RUI: Investigation of Heavy Quark Energy Loss in Relativistic Nucleus-Nucleus Collisions at the CERN LHC

大爆炸后不久，宇宙由一种叫做夸克和胶子的自由粒子等离子体组成。随着宇宙的膨胀和冷却，夸克和胶子凝聚成质子和中子，它们现在构成了所有原子的核心。这种从高温致密等离子体到正常物质气体的相变类似于蒸汽凝结成液态水的相变。科学家们利用大型粒子加速器，在实验室中以非常高的能量碰撞金或铅原子，并研究这种不寻常物质状态的有趣特性，从而重现了这种亚原子汤。相对论重离子对撞机（RHIC）实验中最重要的发现之一是，致密物质对碰撞中产生的高能夸克和胶子是不透明的。这些“粒子”在离开碰撞区时遭受了巨大的能量损失，在介质中沉积了很大一部分初始能量。这种能量损失的强度与夸克胶子等离子体的密度直接相关，并根据部分子的类型而变化。从RHIC的观察来看，较重的夸克与夸克胶子等离子体的耦合似乎比先前预期的更强。高能电子是由重夸克产生的粒子衰变产生的，所以它们出现在组成观测到的喷流的粒子群中，是喷流起源于重夸克的有力证据。这些电子喷流的能量损失可以用来研究夸克胶子等离子体的性质。位于瑞士的欧洲核子研究中心大型强子对撞机（LHC）将以比RHIC高30倍的能量碰撞原子核，产生更热、密度更大、寿命更长的介质。这个RUI项目将利用ALICE实验，利用重夸克喷流的能量损失作为探针来探索这种物质的性质。参与本实验的本科生将接受高能核物理学最前沿的最先进的数据收集、还原和分析技术的培训。他们将能够将这些技能应用于各种各样的职业，无论他们是否选择攻读基础科学的高级学位。他们的贡献还将帮助我们对宇宙基本组成部分之间的基本相互作用产生新的见解，从而更深入地了解我们周围的世界。

Shortly after the Big Bang, the Universe was composed of a plasma of free particles called quarks and gluons. As the Universe expanded and cooled, the quarks and gluons condensed into the protons and neutrons which now make up the cores of all atoms. This phase transition from a hot, dense plasma to a gas of normal matter is similar to that of steam condensing into liquid water. Using large particle accelerators, scientists are recreating this subatomic soup in the laboratory by colliding gold or lead atoms at very high energies and studying the intriguing properties of this unusual state of matter. One of the most important discoveries to come from experiments at the Relativistic Heavy Ion Collider (RHIC) is that the dense matter is opaque to very high energy quarks and gluons produced in the collisions. These `partons' suffer tremendous energy loss as they make their way out of the collision zone, depositing a large fraction of their initial energy in the medium. The strength of this energy loss is directly related to the density of the quark gluon plasma and varies according to the type of parton. From observations at RHIC, the heavier quarks appear to be more strongly coupled to the quark gluon plasma than was previously expected. High energy electrons are produced by the decays of particles made from heavy quarks, so their presence within the cluster of particles that comprise an observed jet is strong evidence for the jet to have originated from a heavy quark. The energy loss of these electron-jets can be used to investigate the properties of the quark gluon plasma.The CERN Large Hadron Collider (LHC) in Switzerland will collide nuclei at energies 30 times higher than at RHIC, producing an even hotter, denser, longer-lived medium. This RUI project will utilize the ALICE experiment to explore the properties of this matter using the energy loss of heavy quark jets as a probe. Undergraduate students working on this experiment will be trained in the most advanced data collection, reduction and analysis techniques at the cutting edge of high energy nuclear physics. They will be able to apply these skills in a wide variety of careers, whether they choose to pursue an advanced degree in basic science or not. Their contributions will also help us develop new insights into the fundamental interactions among the basic building blocks of the universe, leading to a deeper understanding of the world around us.