A Search for New Meson and Baryon Resonances

这里提出的研究主要针对两个项目。第一个是寻找一种被称为标量介子的粒子，它与一种被称为“胶球”的理论粒子具有相同的量子数。后者被推测为只有胶子的束缚系统，胶子是QCD（量子色动力学）理论中携带力的粒子。在实践中，真实粒子是标量介子和假想胶球的量子力学混合物，因此研究标量介子的性质与QCD的预测有直接的联系。在一些强子束实验中已经观察到标量介子，但在杰斐逊实验室提出的光子束实验中，这些介子的证据很少。该研究项目将提供杰斐逊实验室CLAS12探测器产生的标量介子速率的确定结果。第二个项目是强子束实验，将在日本的J-PARC设施进行。本实验将探索两个介子被检测到的最终态的产生速率。这种类型的最后一次数据是在20世纪70年代获得的，现在需要这种最终状态的精确数据作为核子共振理论计算的输入。核子共振是质子的激发态，它可以衰变成一个质子和一个或多个介子（或其他粒子）。核子共振谱很重要，因为它告诉我们夸克是如何在质子内部相互作用的。核子共振谱现在可以用一种叫做点阵量子cd的理论技术来计算，这种技术是基于量子cd理论的。理解QCD（量子色动力学）理论是当今核物理学最重要的方面之一。QCD负责质子内夸克的结合，也负责原子核内质子和中子的结合。因此，QCD本质上是一种理论，可以更好地理解核能和其他核应用。虽然今天核过程的应用，如核医学，可以从现象学的角度来理解，但未来的应用很可能取决于对QCD的理解。基于QCD理论的计算是困难的，需要大型计算机，而且这种复杂的计算需要实验测试。这里提出的研究就是这样一个实验测试，可以更好地理解核力。这项研究产生的其他更广泛的影响是培养研究生在构建前沿仪器和计算分析方面的能力。

The research proposed here is primarily for two projects. The first is a search for a type of particle known as a scalar meson, which has the same quantum numbers as a theoretical particle called the "glueball". The latter is conjectured to be a bound system of only gluons, which are the force-carrying particles in the theory of QCD (quantum chromodynamics). In practice, real particles are a quantum-mechanical mixture of scalar mesons and the hypothetical glueball, so studying the properties of the scalar mesons gives a direct connection with the predictions of QCD. Scalar mesons have been observed in some hadron-beam experiments, but there is scant evidence of these mesons in photon-beam experiments like the ones proposed at Jefferson Lab. This research project will provide definitive results on scalar meson rates produced at the CLAS12 detector at Jefferson Lab. The second project is a hadronic-beam experiment to be carried out at the J-PARC facility in Japan. This experiment will explore the production rate of final states where two pi-mesons are detected. The last data of this sort was taken back in the 1970s, and now precise data for this final state are needed as input to theoretical calculations of nucleon resonances. A nucleon resonance is an excited state of the proton, which can decay into a proton and one or more pi-mesons (or other particles). The nucleon resonance spectrum is important because it tells us about how quarks interact with each other inside the proton. The nucleon resonance spectrum can now be calculated using a theoretical technique called lattice QCD, which is based on the theory of QCD.Understanding the theory of QCD (quantum chromodynamics) is one of the most important aspects of nuclear physics today. QCD is responsible for the binding of quarks inside the proton, and also for the binding of protons and neutrons inside the nucleus. Hence, QCD is essentially the theory that leads to a better understanding of nuclear energy and other nuclear applications. While today's applications of nuclear processes, such as nuclear medicine, can be understood in terms of phenomenology, the applications of the future may well depend on an understanding of QCD. Calculations based on the theory of QCD are difficult, requiring large computers, and such complex calculations need to be tested experimentally. The research proposed here is one such experimental test that can lead to a better understanding of the nuclear force. Other broader impacts resulting from this research are the training of graduate students in building leading-edge instrumentation and in computational analysis.