The hadron spectrum from QCD sum-rules

粒子物理学是在已知最小距离尺度上研究物质和力的学科。 当我们距离越来越近时，就会出现一定的层次结构：物质由分子组成，分子由原子组成，原子由电子和原子核组成，原子核由质子和中子组成。 20 世纪 70 年代人们认识到质子和中子本身是由更小的粒子（称为夸克）构成的。 将夸克结合在一起的力称为强核力，相应的物理理论称为量子色动力学（QCD）。 除了质子和中子之外，夸克组合也是可能的，所产生的束缚态统称为强子。 目前粒子物理学中正在研究的一个重要问题是试图根据每个强子所包含的夸克的已知特性来预测这些强子的特性。 这些属性包括质量、寿命和衰变模式。 特别是，我正在研究一类尚未发现的粒子，称为混合粒子，其存在是由理论预测的。 然而，此类颗粒尚未在实验中得到最终鉴定。

Particle physics is the study of matter and forces at the smallest known distance scales. As we move to smaller and smaller distances, a certain hierarchy emerges: matter is made of molecules, molecules are made of atoms, atoms are made of electrons and nuclei, and nuclei are made of protons and neutrons. It was realized in the 1970's that protons and neutrons themselves are made of even smaller particles called quarks. The force responsible for holding the quarks together is called the strong nuclear force and the corresponding physical theory is called quantum chromodynamics (QCD). Quark combinations aside from protons and neutrons are also possible, and the resulting bound states are collectively referred to as hadrons. An important problem currently being researched in particle physics is that of trying to predict the properties of these hadrons based on known properties of the quarks that each contains. Such properties include mass, lifetime, and decay modes. In particular, I am investigating an as yet undiscovered class of particles called hybrids whose existence is predicted by theory. However, such particles have yet to be conclusively identified in experiment.