A Theoretical Study of Hadronic Interactions and the Structure of the Nucleon

0070368在这项提案中，有两个主要的主题需要研究。第一个涉及质子和中子的夸克子子结构，以及相关的重子。我们正在研究电荷对称性的有效性，即质子中的上夸克和中子中的下夸克的行为应该是相同的。这种近似的对称性在核物理中得到了很好的保存，但我们表明，以前的实验似乎需要在夸克水平上显著偏离电荷对称性。对实验数据的重新分析表明，电荷对称性对于高能物理中的高精度是有效的。我们还建议研究夸克在高能下“碎片化”成重子的过程。我们想知道这些过程是否依赖于产生重子的夸克的类型或“味道”。我们正在为这一过程开发一个模型，并研究兰姆达超子的产生。兰姆达粒子最简单的模型由一个向上、向下和奇怪的夸克组成。人们通常认为，向上夸克、向下夸克和奇异夸克对导致兰布达粒子碎裂的贡献是一样的。我们的初步研究表明，它与这个简单的“味道对称”模型有很大不同。我们可以用简单的定性术语解释为什么这个模型应该是错误的，并且我们预测在哪里应该发生大的味道对称性破坏。我们还建议研究二维系统中粒子的束缚态和散射性质。我们特别感兴趣的是横向尺寸与粒子波长处于同一数量级的系统。在这些情况下，结合和散射是由波效应主导的。我们最近出版了一本关于这个主题的书(《二维系统中的绑定和散射》，Londergan，Carini和Murdock，Springer-Verlag，1999)。我们已经证明，我们的工作与量子线中电子的性质、波导中的受限电磁模式以及被称为光子晶体的光学系统中的受限和传播态有关。在这项建议中，我们将重点讨论“缺陷态”的性质，当人们从一个有限的周期系统开始，然后改变一个或多个产生该周期系统的细胞的性质时，就会发现这些“缺陷态”。首席研究员是印第安纳大学核理论中心的主任。

0070368Londergan There are two major topics to be studied in this proposal. The first deals with the quark sub-structure of protons and neutrons, and related baryons. We are studying the validity of charge symmetry, which states that up quarks in the proton and down quarks in theneutron should behave in identical ways. This approximate symmetry is very well preserved in nuclear physics, but we showed that previous experiments appeared to require significant deviations fromcharge symmetry at the quark level. A re-analysis of the experimental data suggests that charge symmetry is valid to a high degree of precision in high energy physics. We also propose to investigate the process by which quarks produced at high energies ``fragment'' into baryons. We want to see whether these processes depend on the type, or ``flavor,'' of quark which produces the baryon. We are developing a model for this process, and looking at the production of Lambda hyperons. The simplest model for the Lambda particle consists of an up, down and strange quark. It is customary to assume that up, down and strange quarks contribute equally to the fragmentation leading to a Lambda particle. Our preliminary investigations suggest significant differences from this simple ``flavor symmetric'' model. We can explain in simple qualitative terms why this model should be wrong, and we predict where large flavor symmetry violation should occur. We also propose to investigate bound state and scattering properties for particles in two dimensional systems. We are particularly interested in systems whose transverse dimensions are of the same order as the particle wavelength. In these cases, binding and scattering are dominated by wave effects. We have recently published a book on this subject ("Binding and Scattering in Two-Dimensional Systems", Londergan, Carini and Murdock, Springer-Verlag, 1999). We have shown that our work is relevant to the properties of electrons in quantum wires, confined electromagnetic modes in waveguides, and confined and propagating states in optical systems called ``photonic crystals.'' In this proposal we will focus on the properties of ``defect states,'' which are found when one starts with a finite periodic system, and then changes the properties of one or more of the cells producing the periodic system. The principal investigator is Director of the Indiana University Nuclear Theory Center.