Beyond the Conventional Quark Model: Theoretical Studies of QCD Exotics

超越传统夸克模型：QCD 奇异物质的理论研究

• 批准号: SAPIN-2021-00024
• 负责人: Steele, Thomas
• 金额: $ 2.06万
• 依托单位: University of Saskatchewan
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=763198
• 关键词: Beyond; Conventional; Quark; Model; Theoretical

The conventional quark model classifies mesons as quark-antiquark ($q\bar q$) states and baryons as $qqq$ three-quark states. Although the conventional quark model represents the simplest combinations of quarks that can form colour singlets, there is a rich range of other colour-singlet possibilities such as gluonium (consisting entirely of gluons), hybrids (a conventional hadron combined with gluonic content), and multiquark states such as four-quark $q\bar q q\bar q$ mesons and pentaquark $qqq\bar q q$ baryons. These configurations that lie beyond the conventional quark model are collectively known as exotic hadrons. Until 2003, evidence for exotic hadrons was limited to hints of gluonium and a hybrid within the light mesons. However, the 2003 discovery of the X(3872) marked the beginning of a new era in hadron spectroscopy with the discovery of a multitude of XYZ mesons that cannot be described within the conventional quark model.  The long-term passion of my research program is to advance our understanding of exotic hadrons from the theoretical perspective of quantum chromodynamics (QCD): the fundamental theory of the strong interactions. Despite intense theoretical and experimental activity, the internal structure of the XYZ mesons remains an open question. Scenarios for four-quark states include meson-meson molecules, diquark-antidiquark clusters binding into tetraquarks, and hadro-quarkonium with a heavy quark-antiquark core and a cloud of light quarks. These distinct forms of quark internal clustering are expected to manifest themselves in hadronic properties. One of the key themes in the proposed research is to develop and use new QCD sum-rule operators consisting of meson or diquark operators at separate spacetime points to model the internal molecular or tetraquark structure. The goal is to determine the effect of the internal structure on hadronic properties to gain new insights on possible internal configurations. Another main theme of the proposed research is to advance the precision of our theoretical calculations for exotic hadrons to ensure that important physics insights are not obscured by theoretical uncertainties. The vast majority of QCD sum-rule studies of exotics have been performed at leading order, so the proposed research will examine higher-loop effects on the mass spectrum and decays in a variety of exotic systems including hybrid mesons, multiquark states, and hybrid baryons. Mixed interpretations involving hybrid, quark-antiquark, and multi-quark components will be an area of investigation. My research program has pushed the boundaries of QCD sum-rule analytic calculations for exotic hadrons, and the next frontier is the use of sector decomposition methods for numerical loop-integration techniques implemented in pySecDec. Combined with novel theoretical approaches, the proposed research will pioneer the use of these numerical methods in QCD sum-rule studies of exotic hadrons.

传统夸克模型将介子分类为夸克反夸克 ($q\bar q$) 态，将重子分类为 $qqq$ 三夸克态。丰富的其他颜色单线态可能性，例如钍（完全由胶子组成）、混合体（强子与常规胶子含量相结合）和多夸克态例如四夸克 $q\bar q q\bar q$ 介子和五夸克 $qqq\bar q q$ 重子 这些超出夸克模型的配置统称为奇异强子 直到 2003 年，奇异强子的证据仅限于。然而，2003 年 X(3872) 的发现标志着铍和轻介子混合体的开始。强子光谱学的新时代，发现了许多无法在传统夸克模型中描述的 XYZ 介子​我的研究项目的长期热情是从量子色动力学的理论角度增进我们对奇异强子的理解（ QCD）：强相互作用的基本理论尽管有大量的理论和实验活动，但 XYZ 介子的内部结构仍然是一个悬而未决的问题，四夸克态包括介子-介子分子，双夸克-反双夸克星团结合成四夸克，以及具有重夸克-反夸克核心和轻夸克云的强夸克星团，这些不同形式的夸克内部星团预计将在强子特性中体现出来。研究的目的是开发和使用由不同时空点的介子或双夸克算子组成的新QCD和规则算子来模拟内部分子或四夸克结构，目标是确定内部的影响。该研究的另一个主题是提高我们对奇异强子的理论计算的精度，以确保重要的物理见解不会被绝大多数 QCD 的理论不确定性所掩盖。外来物的和规则研究已经在领先顺序上进行，因此拟议的研究将研究各种外来系统（包括混合介子、多夸克态和混合重子）中的质谱和衰变的高环效应。混合、夸克-反夸克和多夸克成分将是一个涉及的研究领域，我的研究计划突破了奇异强子的 QCD 和规则分析计算的界限，下一个前沿是扇区分解方法的使用。 pySecDec 中实现的数值循环积分技术与新颖的理论方法相结合，所提出的研究将开创这些数值方法在奇异强子的 QCD 和规则研究中的应用。