Nucleon Structure and Nuclear Force Studies

这项研究经费将用于两个主要的研究领域。这两个领域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，该小组将研究核子的结构，即中子和质子的结构。这里的主要项目是研究中子内部电荷的分布。虽然中子不带净电荷，但组成中子的三个夸克都带电荷：“上”夸克带正电荷，两个“下”夸克带负电荷，三个夸克的电荷之和为零。由于上夸克更靠近中子中心，下夸克更靠近表面，所以中子内部的电荷分布是中心附近正电荷较多，表面附近负电荷较多。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的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固有角动量，即自旋的起源。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STAR探测器系统上进行了几年；虽然质子的总自旋是已知的，但从组成质子的夸克的相互作用和运动来看，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更清晰的质子结构图像。第二个主要研究领域是对原子核“相关对”结构的研究。在核结构的主流模型中，中子和质子彼此独立地在核内稳定的量子轨道上运动，就像电子围绕核的轨道一样。这个被称为核壳模型的模型的开发者在1963年分享了诺贝尔奖。布鲁克海文国家实验室（Brookhaven National Laboratory）和托马斯·杰斐逊实验室（Thomas Jefferson Laboratory）最近的研究表明，在大约20%的时间里，一个给定的中子或质子，不是在一个独立的轨道上运动，而是以高速背靠背运动的一对粒子的一部分。它们被称为“相关对”，因为它们的速度大小相似，但却是背靠背的。早期的研究得出了一个令人着迷的结果：中子-质子对比中子-中子对或质子-质子对出现的频率高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核，并在比以前的工作中探索的更大的速度范围内观察相关对。这项研究的更广泛影响包括通过核物理期刊传播的对物理宇宙的更多了解，以及对工业、医学物理和学术界所需的博士级物理学家的培训。

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.