Nucleon Structure and Nuclear Force Studies

这项研究拨款将探索两个主要研究领域。这两个领域都将为肯特州立大学的博士生提供培训和论文研究数据。首先，该小组将研究核子结构，即中子和质子的结构。这里的主要项目是研究中子内部的电荷分布。虽然中子没有净电荷，但组成中子的三个夸克都有电荷：上夸克带正电荷，两个下夸克带负电荷，三个夸克的电荷总和为零。由于上夸克倾向于更接近中子的中心，而下夸克更多地在表面，因此在中子内部有一种电荷分布，在中心附近有更多的正电荷，在表面附近有更多的负电荷。这种电荷分布的精确测量将在托马斯·杰斐逊实验室进行，使用肯特州立大学开发的设备。这些测量具有相当重要的科学意义，因为它们为试图描述中子夸克结构的理论模型提供了约束。第二个项目是研究质子的本征角动量的起源，即自旋。这个项目已经在布鲁克海文国家实验室的相对论重离子对撞机(RHIC)的恒星探测器系统上进行了几年；尽管质子的总自旋是已知的，但就组成质子的夸克的相互作用和运动而言，它的起源还不是很清楚。用RHIC加速器进行的测量现在提供了关于质子结构的更清晰的图像。第二个主要研究领域是研究原子核的“关联对”结构。在原子核结构的主导模型中，中子和质子在原子核内部的稳定量子轨道上相互独立地运动，就像围绕原子核的电子的轨道一样。这种被称为核壳模型的模型的开发者分享了1963年的诺贝尔奖。布鲁克海文国家实验室和托马斯·杰斐逊实验室最近的研究表明，在大约20%的时间里，给定的中子或质子不是在独立的轨道上运动，而是一对背靠背高速运动的粒子的一部分。它们被称为“相关对”，因为它们的速度在大小上相似，但背靠背。这项早期研究的一个有趣结果是，中子-质子对出现的频率是中子-中子对或质子-质子对的20倍。这一发现对理解中子星具有重要意义。这些结果来自于对碳核的研究。该小组将把这项工作扩展到氦原子核，并在比之前的工作中探索的更大范围内观察相关的速度对。这项研究的更广泛的影响包括通过被引用的核物理期刊增加对物理宇宙的理解，以及培训工业、医学物理和学术界所需的博士级物理学家。

There are two main research areas that will be explored with this research grant. Both of these areas will provide training and dissertation research data for Ph.D. students from Kent State. First, the group will be investigating the structure of the nucleon, i.e., of the neutron and proton. The primary project here is to study the distribution of electrical charge inside the neutron. Although the neutron has no net electrical charge, the three quarks that make up the neutron have electrical charge: plus charge for the "up" quark, and minus charge for the two "down" quarks, with the charges of all three summing up to zero. Since the up quark tends to be closer to the center of the neutron, and the down quarks more on the surface, there is a distribution of charge within the neutron, with more plus charge near the center, and more minus charge near the surface. Precision measurements of this charge distribution will be made at Thomas Jefferson Laboratory, using equipment developed at Kent State. These measurements are of considerable scientific importance, because they provide constraints on theoretical models attempting to describe the quark structure of the neutron. The second project is to study the origin of the intrinsic angular momentum, known as the spin, of the proton. This project has been underway for several years with the STAR detector system at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory; although the total spin of the proton is known, its origin in terms of the interactions and motions of the quarks that makeup the proton is not well understood. Measurements performed with the RHIC accelerator are now providing a clearer picture of the structure of the proton.The second main area of research is the study of the "correlated pair" structure of nuclei. In the dominant model of nuclear structure, the neutrons and protons move independently of each other in stable quantum orbits inside the nucleus, much like the orbits of the electrons surrounding the nucleus. The developers of this model, called the nuclear shell model, shared the Nobel Prize in 1963. Recent research at Brookhaven National Laboratory and Thomas Jefferson Laboratory has shown that about 20% of the time, a given neutron or proton, instead of moving in an independent orbit, will be part of a pair of particles moving back-to-back at high velocity. These are called "correlated pairs" because their velocities are similar in size, but back-to-back. A fascinating result from that earlier research is that neutron-proton pairs occur 20 times more often than neutron-neutron pairs or proton-proton pairs. This finding has important implications for understanding neutron stars. These results came from the study of the carbon nucleus. The group will be extending that work to the helium nucleus, and observing correlated pairs for a larger range of velocities than were explored in previous work. The broader impacts of this research include an increased understanding of the physical universe distributed through refereed journals of nuclear physics and the training of doctoral-level physicists needed in industry, medical physics, and academia.