Studies of the Quark-Gluon Plasma with STAR and CMS at UC Davis

加州大学戴维斯分校利用 STAR 和 CMS 进行夸克-胶子等离子体研究

• 批准号: 1404281
• 负责人: Daniel Cebra
• 金额: $ 102万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-07-15 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1404281&HistoricalAwards=false
• 关键词: Studies; Quark; Gluon; Plasma; STAR

The study of the strong nuclear force under extremely high temperature and energy density is one of the key areas of investigation in nuclear physics. The theoretical framework of the strong force is Quantum Chromodynamics (QCD), whose fundamental particles are the quarks and gluons. These in turn build up protons and neutrons, which are understood to be the low-energy phase of quarks, bound by the strong nuclear force. At the very high temperatures reached in relativistic heavy ion collisions, the aim of this project to study how protons and neutrons melt into constituent quarks and gluons, which are no longer bound. 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. Given this background, the project focuses on the experimental measurement of three distinct thermodynamic properties of this novel state of nuclear matter with the STAR detector at the Relativistic Heavy Ion Collider and the CMS experiment at the Large Hadron Collider at CERN. 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 proton-proton, proton-nucleus, and nucleus-nucleus 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, and thereby exploring the transition between normal nuclear matter and QGP matter. The third goal is to study the density of the medium using events in which a neutral electroweak boson, the Z0, is produced in coincidence with a quark jet. The Z0 is unaffected by the QGP, providing a clean estimate of the transverse momentum of the quark jet. As the partner jet traverses the dense QGP medium and loses energy, these Z0 + quark jet events are one of the best ways to study the energy loss of quarks.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 our own graduate students to become leaders in these activities, since many are women and underrepresented minorities, and are therefore excellent role models.

在极高温度和能量密度下的强核力研究是核物理研究的重点领域之一。强作用力的理论框架是量子色动力学（QCD），其基本粒子是夸克和胶子。这些物质又会产生质子和中子，它们被认为是夸克的低能相，被强核力束缚。 在相对论重离子碰撞达到的非常高的温度下，该项目的目的是研究质子和中子如何熔化成不再受束缚的夸克和胶子。 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。该领域正朝着定量理解QGP的热力学性质。在此背景下，该项目的重点是用相对论重离子对撞机上的星星探测器和欧洲核子研究中心大型强子对撞机上的CMS实验，对这种新的核物质状态的三种不同的热力学性质进行实验测量。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。该小组将研究质子-质子、质子-核和核-核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。本研究是利用星星，通过改变碰撞能量，从而探索正常核物质与QGP物质之间的跃迁。第三个目标是利用中性电弱玻色子（Z 0）与夸克喷注同时产生的事件来研究介质的密度。Z 0不受QGP的影响，提供了一个清晰的夸克喷注横向动量的估计。当伙伴喷流穿过稠密的QGP介质并损失能量时，这些Z 0+夸克喷流事件是研究夸克能量损失的最佳方法之一。这项工作的更广泛影响针对代表性不足的少数民族和妇女。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我们自己的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。