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.

Although the conventional quark model represents the simplest combinations of quarks that can form colour singles, there is a rich range of other colour-singlet possibilities such as glutium (consisting entirely of glutes), hybrids (a conventional hadron combined with glutonic content), and multiquark states Such as four-quark $q\bar q q\bar q$ mesons and pentaquark $qqq\bar q q$重子。这些超出传统夸克模型以外的配置被共同称为异国黑龙。直到2003年，外来had子的证据仅限于轻微介体中的glutium和杂种。然而，2003年发现X（3872）的发现标志着放火体光谱的新时代的开始，发现了许多在常规夸克模型中无法描述的众多XYZ介子。我的研究计划的长期热情是从量子染色体动力学（QCD）的理论角度来提高我们对异国黑龙的理解：强烈互动的基本理论。尽管有强烈的理论和实验活动，但XYZ介子的内部结构仍然是一个悬而未决的问题。四夸克国家的场景包括梅森 - 梅森分子，diquark-antidiquark群集结合到tetraquarks中，以及带有重夸克 - 易夸克核心的夸夸王子和一云的夸克夸克。这些不同形式的夸克内部聚类预计将在宽容性特性中表现出来。拟议研究的主要主题之一是开发和使用新的QCD Sum-rule运算符，这些操作员在单独的时空点上由介子或diquark运算符组成，以模拟内部分子或四夸克结构。目的是确定内部结构对HADRONIC属性的影响，以便对可能的内部配置获得新的见解。拟议的研究的另一个主要主题是提高我们对异国载体的理论计算的精确度，以确保不被理论上的不确定性掩盖重要的物理学见解。绝大多数QCD总规则研究是在领先的顺序上进行的，因此拟议的研究将检查对质谱的更高效果，并在包括混合介子，多Quarkark States和Hybrid Barons在内的各种外来系统中衰减。涉及混合动力，夸克 - 易药和多夸克组件的混合解释将是一个研究领域。我的研究计划已突破了异国黑核的QCD总规则分析计算的界限，下一个前沿是使用PysecDec中实现的数值循环整合技术的扇区分解方法。与新的理论方法相结合，提出的研究将在QCD Sum-Rule-Rule研究中使用这些数值方法。