Nucleon Structure and Nuclear Force Studies

核结构和核力研究

• 批准号: 0354915
• 负责人: Bryon Anderson
• 金额: $ 54万
• 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: 2004
• 资助国家: 美国
• 起止时间: 2004-06-01 至 2008-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0354915&HistoricalAwards=false
• 关键词: Nucleon; Structure; Nuclear; Force; Studies

The general objective of this project is to study the structure of nucleons, i.e., neutrons and protons, and to investigate certain interesting aspects of the nuclear force. It is recognized now that nucleons are not fundamental particles. They are comprised of smaller particles, called quarks. The quarks are held together inside the nucleon by the exchange of particles called gluons. It is generally believed that the quarks and gluons are fundamental particles and are not comprised of even smaller particles. The quarks move inside the nucleon and, by the nature of the uncertainty principle of quantum mechanics, other quark-antiquark pairs are continually being created and destroyed inside the nucleon. The net result is that the nucleon is a fairly complicated collection of various kinds of quarks and the gluons. In order to understand exactly which quarks are there and how they are moving, it is necessary to measure detailed characteristics of the nucleons.One of the goals of this project is to extend earlier measurements of the charge distribution inside the neutron. The neutron is overall electrically neutral, but has a core of positive charge surrounded by an outer region of negative charge. Precise measurement of this charge distribution provides one of the most sensitive tests of what quarks are present in the neutron and how they are moving. This experiment will be performed at the Jefferson National Accelerator Facility in Virginia. Another goal of this project is to try to further our understanding of the source of the intrinsic angular momentum, or spin, of the proton. In a very simple model of the proton, it can be considered to be comprised of just three, so-called, valence quarks, and it is possible to see how these three quarks, with their own intrinsic spins, can combine to give the known spin of the proton; however, a series of experiments performed at electron accelerators in the U.S.A. and Europe have shown that the quark spins actually provide only about 1/3 of the total spin of the proton. The remaining 2/3 must come from the motions of the quarks and from the gluons that are being exchanged between the quarks. This group is involved in a series of experiments to be performed with colliding proton beams at the relativistic heavy-ion accelerator (RHIC) at Brookhaven National Laboratory on Long Island, New York to try to measure the contribution of the gluons to the spin of the proton. Even though the overall spin of the proton is well known, these measurements will, similar to the measurements of the charge distribution of the neutron, enable us to better understand what is happening inside the nucleon. Finally, it is also a goal of this project to perform an experiment to study the short-range nature of the nuclear force inside nuclei. This experiment will be performed at the Jefferson Laboratory and is a follow-up to a similar experiment performed at Brookhaven. That earlier experiment pioneered a technique for taking "snapshots" of two nucleons interacting at very small separation distances, and reconstructing their relative motions. The Jefferson Laboratory experiment will allow us to do this type of reconstruction with much greater precision.

该项目的总体目标是研究核子的结构，即，中子和质子，并研究核力的某些有趣方面。 现在人们认识到核子不是基本粒子。 它们由更小的粒子组成，称为夸克。 夸克在核子内部通过胶子的交换而结合在一起。 一般认为，夸克和胶子是基本粒子，并不是由更小的粒子组成。 夸克在核子内部运动，根据量子力学的不确定性原理，其他夸克-反夸克对在核子内部不断地产生和消灭。 最终的结果是，核子是各种夸克和胶子的相当复杂的集合。 为了准确地了解那里有哪些夸克以及它们是如何运动的，有必要测量核子的详细特征。该项目的目标之一是扩展早期对中子内部电荷分布的测量。 中子总体上是电中性的，但是具有被负电荷的外部区域包围的正电荷的核心。 对这种电荷分布的精确测量提供了对中子中存在哪些夸克以及它们如何运动的最灵敏的测试之一。这项实验将在弗吉尼亚州的杰斐逊国家加速器设施进行。 这个项目的另一个目标是试图进一步了解质子的固有角动量或自旋的来源。 在一个非常简单的质子模型中，它可以被认为是由三个所谓的价夸克组成，并且可以看到这三个夸克如何用它们自己的内在自旋联合收割机给出质子的已知自旋;但是，在此情况下，在美国和欧洲的电子加速器上进行的一系列实验表明，夸克自旋实际上只提供大约1/质子总自旋的3倍。 剩下的2/3必须来自夸克的运动和夸克之间交换的胶子。 该小组参与了一系列实验，这些实验将在纽约长岛布鲁克海文国家实验室的相对论重离子加速器（RHIC）上进行，以测量胶子对质子自旋的贡献。 尽管质子的整体自旋是众所周知的，但这些测量将与中子电荷分布的测量类似，使我们能够更好地了解核子内部发生的事情。 最后，该项目的另一个目标是进行一项实验，研究原子核内部核力的短程性质。 该实验将在Jefferson实验室进行，是在Brookhaven进行的类似实验的后续实验。 早期的实验开创了一种技术，可以拍摄两个核子在非常小的距离上相互作用的“快照”，并重建它们的相对运动。 杰斐逊实验室的实验将使我们能够以更高的精度进行这种类型的重建。