Experimental Studies of the Properties of the QGP and the QCD Phase Diagram

量子色动力学（QCD）是描述强核力的理论框架。通过这种力相互作用的基本粒子是夸克和胶子，它们构成质子和中子，而质子和中子又在所有原子的核心构成原子核。该项目旨在研究在相对论重离子碰撞中达到的极高温度下物质的性质。 该小组将研究质子和中子如何熔化成夸克和胶子，这些夸克和胶子在这些条件下不再受束缚。核物质的这种高温相被称为夸克-胶子等离子体（QGP）。在相对论重离子对撞机和大型强子对撞机上进行的重离子实验为QGP的形成提供了有力的证据。该领域正在朝着定量理解QGP的热力学性质，这项工作将有助于这种理解。该项目的重点是通过星星和CMS实验测量这种新的核物质状态的两种不同的热力学性质。第一个要测量的性质是碰撞最热阶段产生的温度。这是通过对Uppermuson介子的研究来实现的，Uppermuson介子是一种重的“底”夸克的束缚态。在碰撞的早期阶段，即使是重夸克束缚态，如大灾变，也会在碰撞中融化。该小组将研究在pp、pA和AA碰撞中厄普塞隆及其与星星和CMS的激发态的熔化模式。这一测量结果将为高温QGP中夸克解禁闭模型的检验提供重要信息。第二个目标是研究强作用力的热力学相结构。特别是，测试预测的QCD临界点的存在是这一目标的关键组成部分。本研究以星星为研究对象，通过改变对撞机和固定靶碰撞中的碰撞能量，探索正常核物质与QGP物质之间的跃迁。增加固定目标能量扫描是重要的，因为目前的证据表明，临界点可能位于对撞机可获得的最低能量处，并且扫描该跃迁的上方和下方都很重要。这项工作的更广泛影响是针对代表性不足的少数群体和妇女。第一个是通过会议上的指导活动和加州大学戴维斯分校SACNAS分会的支持，将高能核物理学的兴奋传达给墨西哥裔和美洲原住民科学促进协会（SACNAS）的拉丁裔学生。第二个组成部分是通过访问拉丁美洲人口众多的小学和参加高中的“物理学家”方案，向小学和高中学生宣传科学和物理学。最后，项目中的PI将指导本科生，包括NSF REU学生，每年。这些目标的一个关键部分是指导研究生成为这些活动的领导者，因为许多人是妇女和代表性不足的少数民族，因此是优秀的榜样。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Quantum Chromodynamics (QCD) is the theoretical framework that describes the strong nuclear force. The fundamental particles that interact via this force are the quarks and gluons that build up protons and neutrons, which in turn build up the atomic nuclei at the cores of all atoms. This project aims to study the nature of matter at the very high temperatures reached in relativistic heavy ion collisions. The group will study how protons and neutrons melt into constituent quarks and gluons, which are no longer bound under these conditions. This high-temperature phase of nuclear matter is called the Quark-Gluon Plasma (QGP). Heavy-ion experiments at the Relativistic Heavy-Ion Collider and the Large Hadron Collider have produced striking evidence for QGP formation. The field is moving towards a quantitative understanding of the thermodynamic properties of the QGP, and this work will contribute to that understanding. This project focuses on the experimental measurement of two distinct thermodynamic properties of this novel state of nuclear matter with the STAR and the CMS experiments. The first property to be measured is the temperature produced in the hottest stages of the collision. This is done via the study of Upsilon mesons, a bound state of heavy "bottom" quarks. In the hot, early stage of the collision even heavy-quark bound states, like the Upsilon, are expected to melt in the collision. The group will study the melting pattern of Upsilons and their excited states with STAR and with CMS in pp, pA, and AA collisions. This measurement will provide crucial information to test models of the deconfinement of quarks in the high-temperature QGP. The second goal is to study the thermodynamic phase structure of the strong force. In particular, testing the existence of a predicted QCD critical point is a key component of this goal. This study is done with STAR by varying the collision energy both in collider and fixed-target collisions, and thereby exploring the transition between normal nuclear matter and QGP matter. Adding the fixed target energy scan is important because the current evidence suggests that the critical point may lie at the lowest energy accessible to the collider, and it is important to scan both above and below this transition. The broader impacts of this work are aimed at underrepresented minorities and women. The first is to communicate the excitement of high-energy nuclear physics to Latino students at the Society for the Advancement of Chicanos and Native Americans in Science (SACNAS), through mentoring activities at the conference and support of the UC Davis SACNAS chapter. The second component is promotion of science and physics to elementary and high-school students through visits to elementary schools with large Latino populations, and via participation in the Adopt-A-Physicist program for high schools. Finally, the PIs in the project will mentor undergraduates, including NSF REU students, every year. A key part of these goals is the mentoring of graduate students to become leaders in these activities, since many are women and underrepresented minorities, and are therefore excellent role models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.