Nucleon Structure and Nuclear Force Studies

核结构和核力研究

• 批准号: 0969129
• 负责人: Bryon Anderson
• 金额: $ 46.5万
• 依托单位: Kent State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-01 至 2014-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0969129&HistoricalAwards=false
• 关键词: Nucleon; Structure; Nuclear; Force; Studies

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.

这项研究资助将探索两个主要研究领域。 这两个领域都将为博士提供培训和论文研究数据。 来自肯特州立大学的学生。 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。 尽管中子没有净电荷，但组成中子的三个夸克却带有电荷：“上”夸克带正电荷，两个“下”夸克带负电荷，所有三个夸克的电荷总和为零。 由于上夸克往往更靠近中子中心，而下夸克更靠近中子表面，因此中子内部存在电荷分布，靠近中心的正电荷较多，靠近表面的负电荷较多。 这种电荷分布的精确测量将在托马斯·杰斐逊实验室使用肯特州立大学开发的设备进行。 这些测量具有相当大的科学重要性，因为它们为试图描述中子夸克结构的理论模型提供了限制。 第二个项目是研究质子的固有角动量（称为自旋）的起源。 该项目已使用布鲁克海文国家实验室相对论重离子对撞机 (RHIC) 的 STAR 探测器系统进行了数年；尽管质子的总自旋是已知的，但其构成质子的夸克的相互作用和运动的起源尚不清楚。 使用 RHIC 加速器进行的测量现在可以更清晰地了解质子的结构。第二个主要研究领域是研究原子核的“相关对”结构。 在核结构的主要模型中，中子和质子在核内稳定的量子轨道上彼此独立地运动，就像电子围绕核的轨道一样。 这个模型（称为核壳模型）的开发者于 1963 年分享了诺贝尔奖。布鲁克海文国家实验室和托马斯·杰斐逊实验室的最新研究表明，大约 20% 的情况下，给定的中子或质子不是在独立轨道上运动，而是成为一对高速背对背运动的粒子的一部分。 这些被称为“相关对”，因为它们的速度大小相似，但背靠背。 早期研究的一个令人着迷的结果是，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。 这一发现对于理解中子星具有重要意义。 这些结果来自对碳核的研究。 该小组将把这项工作扩展到氦核，并观察相关对的速度范围比之前的工作中探索的更大。 这项研究的更广泛影响包括通过核物理审稿期刊增加对物理宇宙的理解，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。