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

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，它们构成了质子和中子，而质子和中子又构成了组成所有原子的原子核。该项目旨在研究极高温度(约比太阳核心热一百万倍)下物质的性质，在极高温度下，核物质达到一个称为夸克胶子等离子体(QGP)的阶段。相对论重离子对撞机(RHIC)和大型强子对撞机(LHC)达到了这些极高的温度，这为QGP的形成提供了惊人的证据。在RHIC，加州大学戴维斯分校核物理组(UCD NPG)将研究高密度区相变的热力学性质，利用对撞机的多功能性来访问QCD相图的不同区域，特别关注临界点的存在。UCD NPG将研究固定目标碰撞和束-束碰撞，以扫描相图中已发现临界点迹象的区域。在大型强子对撞机上，UCD NPG将使用重夸克束缚态来研究QGP在最高可用温度下的性质，这一温度因LHC能量升级到每核子对5.5TeV而变得更高。重夸克素态，如底-反底或反魅力-反魅力，对QGP相中预期的QCD势的变化很敏感。该奖项将支持对底夸克态和魅力夸克态的修改模式的研究，这些模式允许表征介质的温度和QGP阶段QCD势的变化。UCD NPG将通过由NSF资助的巨幕电影《宇宙的秘密》来促进科学教育，这部电影由Co-Pi Calderon de la Barca讲述并主演，该电影以这个团体的学生和作品为特色。通过公开放映这部电影并现场问答，UCD NPG小组将教育公众了解大型强子对撞机所做的科学，并将鼓励儿童，特别是女孩和代表性不足的儿童，考虑在STEM从事职业。UCD NPG将在整个项目中培训和指导REU和UCD本科生。UCD NPG在与RHIC固定目标计划有关的关键作用中，将对模拟宇宙辐射的碰撞进行研究。这些研究对NASA的空间辐射防护计划有直接影响，该计划旨在了解和减轻长期太空任务中宇宙辐射的影响。该项目的范围涉及RHIC和大型强子对撞机的研究。在RHIC和星实验的定靶程序覆盖的能量范围内，从3-200GeV，UCD NPG将研究QCD物质的相图。强子谱和重子数涨落的分析将被用来描述在每个测量能量下的QCD环境。这些研究将使寻找RHIC扫描的能量范围低端附近的相图的推测临界点成为可能。该项目的这一部分将促进我们对这种临界点的存在以及它在强相互作用相图中的位置的认识。在大型强子对撞机可用的最高能量下，UCD NPG将通过CMS实验研究重夸克子态。大型强子对撞机的能量升级带来了更高的能量和亮度，这将使研究在同一碰撞中有两个夸克尼亚介子的事件成为可能。同时产生Upsilon和J/psi的事件将提供一个新的窗口来研究QGP，以及QCD势如何在强相互作用的高温、去禁闭阶段影响这些态的形成。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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 nuclei that make up all atoms. This project aims to study the nature of matter at very high temperatures (about a million times hotter than the sun’s core), where nuclear matter reaches a phase called the Quark-Gluon Plasma (QGP). These extremely high temperatures are reached at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), which have produced striking evidence for QGP formation. At RHIC, the UC Davis Nuclear Physics Group (UCD NPG) will study the thermodynamic properties of the transition in the high-density regime, taking advantage of the versatility of the collider to access different regions of the QCD phase diagram, with particular focus on the existence of a critical point. The UCD NPG will study both fixed-target collisions and beam-beam collisions to scan areas of the phase diagram where indications of the critical point have been found. At the LHC, the UCD NPG will use heavy-quark bound states to study the properties of the QGP at the highest available temperatures, made even higher by the upgrade of the LHC energy to 5.5 TeV per nucleon pair. Heavy quarkonium states, such as bottom-antibottom or charm-anticharm, are sensitive to the modification of the QCD potential expected in the QGP phase. This award will support studies of the pattern of modifications for the bottom and charm quark states that allow a characterization of the temperature of the medium and of the changes to the QCD potential in the QGP phase. The UCD NPG will promote science education by reaching out to the broadest possible audiences through the NSF-funded giant-screen film “Secrets of the Universe”, narrated and starring Co-Pi Calderon de la Barca, and which features the students and work from this group. Through public screenings of the film with live Q&A sessions, the UCD NPG group will educate the public about the science done at the LHC and will encourage children, particularly girls and underrepresented kids, to consider pursuing careers in STEM. The UCD NPG will train and mentor REU and UCD undergraduate students throughout the project. The UCD NPG, in its pivotal role pertaining to the RHIC fixed-target program, will conduct a study of collisions that mimic cosmic radiation. Such studies have a direct impact on the NASA space-radiation protection program aimed at understanding and mitigating the effects of cosmic radiation during lengthy space missions.The scope of this project involves studies at RHIC and at the LHC. At the energy range covered by RHIC and the fixed-target program of the STAR experiment, from 3 – 200 GeV, the UCD NPG will study the phase diagram of QCD matter. Analyses of hadron spectra and baryon-number fluctuations will be used to characterize the QCD environment at each measured energy. These studies will enable searches for the conjectured critical point of the phase diagram near the low-end of the energy range scanned by RHIC. This part of the project will advance our knowledge of the existence of such a critical point and its location in the phase diagram of the strong interaction. At the top energy available at the LHC, the UCD NPG will study heavy-quarkonium states with the CMS experiment. The energy upgrade at the LHC, enabling higher energies and luminosities, will allow studies of events with two quarkonia mesons in the same collision. Events where an Upsilon (bottomonium) and J/psi (charmonium) are simultaneously produced will provide a new window to study the QGP, and how the QCD potential affects the formation of these states in the high-temperature, deconfined phase of the strong interaction.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.