The confined gluon: precision spectroscopy with charm quarks

粲偶素系统由一对粲夸克和反粲夸克组成。贝儿和巴巴尔在千禧年之初的实验中发现了一些完全出乎意料的窄共振，称为X、Y和Z，这使得人们对粲偶素的兴趣发生了革命性的变化。尽管近二十年的理论研究，没有清晰的图片的内部机制，这些共振已经出现。本项目的主要目标之一是通过发展和优化用于高精度强子谱蒙特卡罗计算的新技术，对粲偶素谱（包括XYZ态）有新的认识。这些发展将集中在优化创建运营商和Monte Carlo评估其相关函数，以确定在有限体积的低躺状态的频谱，以高精度。在第一次扩展单强子相关函数的技术，并与研究单位的其他项目建立联系后，我们将研究计算一些charmonium状态的宽度所需的多强子相关函数，这些状态低于开放魅力阈值，包括它们的OZI抑制衰变成胶球和轻强子。由于有效的统计抽样方法与创建运营商优化物理目标相结合，混合charmonium状态将被探索。它们位于开粲阈值之上，OZI允许它们衰变为粲介子。我们将在足够大的轻夸克质量下进行弹性散射分析。该项目的另一个主要目标是研究光夸克和胶子在静态夸克间势的轨道激发中的自由度。将与研究股的其他项目密切合作，开发有效计算的新技术。由于静态轻介子对的形成，在组分胶子的存在下基态势的饱和将被详细研究。这种现象被称为断弦。这种扁平化提供了一个连接到粲偶素混合物在重夸克极限的强衰变物理。在这个极限下，玻恩-奥本海默近似通过求解相对论轻夸克和内禀胶子产生的绝热势中的非相对论薛定谔方程来处理杂化粲偶素，这将使用格点QCD计算。在这个项目中开发的混合势的技术可以应用到四夸克势，提供洞察的内部结构的奇异配置的静态源与非平凡的自旋和同位旋。计划在研究股的第二个供资期开展四夸克态势研究。

The charmonium system consists of a charm and anti-charm quark pair. Interest in charmonium underwent a revolution after a number of entirely unexpected narrow resonances, called the X, Y and Zs were discovered by the Belle and BaBar experiments at the start of the millenium. In spite of almost two decades of theory investigations, no clear picture of the internal mechanics of these resonances has emerged. This project aims to develop a robust framework using lattice QCD to calculate properties of charmonium including hadronic decays and to exploit this framework to progress our understanding of recent experimental discoveries.One of the major goal of the project is to get new insight into the charmonium spectrum, including the XYZ states by developing and optimising new techniques for high-precision hadron spectroscopy Monte Carlo calculations. These developments will focus on optimising the creation operators and the Monte Carlo evaluation of their correlation functions to determine the spectrum of low-lying states in finite volume to high precision. After first extending techniques for single-hadron correlation functions and developing links with other projects in the Research Unit, we will investigate the multi-hadron correlation functions needed to compute the widths of some of the charmonium states below the open-charm threshold including their OZI suppressed decays into glueballs and light hadrons. As efficient statistical sampling methods are combined with creation operators optimised for physics goals, hybrid charmonium states will be explored. They lie above the open-charm threshold and their decays into charmed mesons are OZI allowed. We will perform a first scattering analysis in an elastic setting realized for sufficiently large light quark masses.The other major goal of the project will be a study of light-quark and gluon degrees of freedom in orbital excitations to the potential between static quarks. New techniques for efficient computations will be developed, in close collaboration with the other projects of the Research Unit. The saturation of the ground-state potential in the presence of constituent gluons due to the formation of static-light-meson pairs will be examined in detail. This phenomenon is known as string-breaking. This flattening provides a connection to the strong decay physics of charmonium hybrids in the heavy-quark limit. In this limit, the Born-Oppenheimer approximation treats hybrid charmonium by solving the non-relativistic Schrödinger equation in the adiabatic potential generated by the relativistic light quarks and intrinsic gluons, which will be computed using lattice QCD. The technology developed in this project for hybrid potentials can be applied to tetraquark potentials which provide insight into the internal structure of exotic configurations of static sources with non-trivial spin and isospin. Tetraquark potentials are planned for a second funding period of the Research Unit.