Quantifying Key Properties of the Quark-Gluon Plasma at UC Davis

理解强核力及其对物质行为的影响是目前核物理学研究的关键问题之一。我们目前的理解是基于量子色动力学（QCD）的理论框架，量子色动力学的基本粒子是夸克和胶子，它们共同构成质子和中子。核科学的前沿问题之一是了解质子和中子如何融化成它们的组成夸克和胶子，形成一种称为夸克-胶子等离子体（QGP）的状态。这就是相对论重离子碰撞的目标。在相对论重离子对撞机和大型强子对撞机上进行的高能重离子实验提供了QGP形成的诱人证据。我们正从发现阶段转向对QGP物理特性的定量理解，这个项目的重点是对这种新型核物质状态的三种不同特性的实验测量。这个奖项的智力价值可以概括为以下三个目标。首先是通过研究厄普西隆介子来测量碰撞最热阶段产生的温度。在碰撞的早期阶段，即使像厄普西隆这样的重夸克束缚态，如果温度足够高，也会在等离子体中熔化。我们将通过厄普西隆衰变为介电子来研究厄普西隆，并将参与探测器升级以研究介子衰变通道。第二个目标是研究强作用力的热力学相结构，检验QCD临界点的存在性。这是通过改变碰撞能量来实现的，从而探索正常核物质和QGP物质之间的转变。第三个目标是首次在相对论性重离子碰撞中测量中性电弱玻色子Z0。该粒子有望成为重离子碰撞中抛射核初始夸克含量的最干净的参考，因为在双介子衰变通道中研究它时，它不会受到QGP的影响。因此，它可以作为衡量介质其他测量值的最佳标准蜡烛。特别是，对Z0 +射流（后者是一束强相互作用的粒子）产生的联合研究为我们提供了一个研究通道，该通道具有不受干扰的实验标签- Z0 -以及可以探测介质密度的可观察物-伴随射流。这项工作的更广泛影响是针对代表性不足的少数民族和妇女。第一个是通过指导活动、演讲选择和评判以及提供积极反馈，向奇卡诺人和美洲原住民科学促进会（SACNAS）的拉丁裔学生传达高能核物理的兴奋之情。第二个组成部分是通过参观拉丁裔人口较多的小学和参加高中收养物理学家项目，向小学和高中学生推广科学和物理。最后，该项目的pi每年将指导本科生，包括NSF REU学生。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，因为许多是女性和代表性不足的少数民族，因此是优秀的榜样。

Understanding the strong nuclear force and its implications for the behavior of matter is one of the key questions currently under investigation in nuclear physics. Our current understanding is based on the theoretical framework of Quantum Chromodynamics (QCD), whose fundamental particles are the quarks and gluons that together build up protons and neutrons. One of the problems at the frontier of nuclear science is to understand how protons and neutrons melt into their constituent quarks and gluons, forming a state called the Quark-Gluon Plasma (QGP). This is the goal of relativistic heavy-ion collisions. Tantalizing evidence for the formation of QGP has been produced by the highest energy heavy-ion experiments done at the Relativistic Heavy-Ion Collider and the Large Hadron Collider. We are moving from a discovery phase towards a quantitative understanding of the physical characteristics of the QGP, and this project focuses on the experimental measurement of three distinct properties of this novel state of nuclear matter. The intellectual merit for this award can be summarized by the following three goals. The first is to measure the temperature produced in the hottest stages of the collision via the study of Upsilon mesons. In the early stage of the collision even heavy-quark bound states, like the Upsilon, will melt in the plasma if it is hot enough. We will study Upsilons via their decay into dielectrons and will participate in a detector upgrade to study the di-muon decay channel. The second goal is to study the thermodynamic phase structure of the strong force, testing for the existence of the QCD critical point. This is done by varying the collision energy and thereby exploring the transition between normal nuclear matter and QGP matter. The third goal is to measure the neutral electroweak boson, the Z0, for the first time in a relativistic heavy ion collision. This particle promises to be the cleanest reference of the initial quark content of the projectile nuclei in heavy-ion collisions because, when studying it in the di-muon decay channel, it will not be affected by the QGP. It can therefore act as the best standard candle against which to gauge other measurements of the medium. In particular, a joint study of Z0 + jet (the latter a bundle of strongly interacting particles) production gives us a research channel with an experimental tag that is undisturbed - the Z0 - together with an observable that can probe the density of the medium - the accompanying jet.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, presentation selection and judging, and providing positive feedback. 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 student to become leaders in these activities, since many are women and underrepresented minorities, and are therefore excellent role models.