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.

在极高的温度和能量密度下对强核力量的研究是核物理学研究的关键领域之一。强力的理论框架是量子染色体动力学（QCD），其基本颗粒是夸克和胶子。这些反过来又建立了质子和中子，被认为是受强核力量约束的夸克的低能阶段。 在相对论重离子碰撞中达到的高温下，该项目的目的是研究质子和中子如何融化成不再结合的组成夸克和胶子。 核物质的这种高温期称为夸克 - 胶原等离子体（QGP）。相对论重离子对撞机和大型强子对撞机的重型离子实验为QGP形成提供了惊人的证据。该领域正在朝着对QGP热力学特性的定量理解。鉴于此背景，该项目的重点是对这种新型核物质的三种不同热力学特性的实验测量，而在相对论重离子对撞机和CERN大型强子对撞机的CMS实验处的星形检测器和CMS实验。要测量的第一个特性是在碰撞最热阶段产生的温度。这是通过对Upsilon Meson的研究来完成的，Upsilon Meson是一个重型“底部”夸克的结合状态。在碰撞的炎热，早期，甚至像Upsilon这样的重夸克的国家，也有望在碰撞中融化。该小组将研究Upsilons及其激发态的熔融模式，并在Proton-Proton，Proton-Nucleus和Nucleus-Nucleus碰撞中使用CMS和CMS研究。这种测量将为高温QGP中夸克的解料的测试模型提供至关重要的信息。第二个目标是研究强力的热力学相结构。特别是，测试预测的QCD临界点的存在是该目标的关键组成部分。这项研究是通过改变碰撞能量来完成的，从而探索了正常核物质和QGP物质之间的过渡。第三个目标是使用事件研究培养基的密度，在这种事件中，中性电孔玻色子（Z0）与夸克射流偶然产生。 Z0不受QGP的影响，提供了夸克射流横向动量的干净估计。当合作伙伴穿越密集的QGP培养基并失去能量时，这些Z0 + Quark Jet事件是研究Quark能源损失的最佳方法之一。这项工作的更广泛影响旨在旨在代表性不足的少数民族和妇女。首先是通过在UC Davis Sacnas分会的会议上指导活动和支持，向奇卡诺斯和美洲原住民学会（SACNAS）促进的拉丁裔学生的兴奋传达给拉丁裔学生。第二部分是通过访问具有庞大的拉丁裔人群的小学，并通过参加高中的收养物理学计划，向小学和高中生促进科学和物理学。最后，该项目中的PI每年将指导包括NSF REU学生在内的本科生。这些目标的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，因为许多是女性和代表性不足的少数群体，因此是出色的榜样。