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

[00:70368]在这个提案中有两个主要的主题需要研究。第一部分讨论质子和中子的夸克子结构，以及相关的重子。我们正在研究电荷对称的有效性，它指出质子中的上夸克和中子中的下夸克应该以相同的方式表现。这种近似对称在核物理学中保存得很好，但我们表明，以前的实验似乎需要在夸克水平上明显偏离电荷对称。对实验数据的重新分析表明，电荷对称性在高能物理中具有很高的精度。我们还建议研究夸克在高能时产生的“碎片”变成重子的过程。我们想看看这些过程是否取决于产生重子的夸克的类型或“味道”。我们正在为这个过程开发一个模型，并观察Lambda超子的产生。λ粒子最简单的模型由一个上、下和奇异夸克组成。通常认为，上、下和奇夸克对导致λ粒子的分裂的贡献是相等的。我们的初步调查表明，与这种简单的“风味对称”模型存在显著差异。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，我们预测在哪里会发生大的风味对称性破坏。我们还建议研究二维系统中粒子的束缚态和散射特性。我们对横向尺寸与粒子波长相同的系统特别感兴趣。在这种情况下，结合和散射主要受波效应的支配。我们最近出版了一本关于这个主题的书（“二维系统中的结合和散射”，Londergan， Carini和Murdock， Springer-Verlag, 1999）。我们已经证明，我们的工作与量子线中的电子性质、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状态有关。“在这个提议中，我们将专注于‘缺陷状态’的特性，当一个人从一个有限周期系统开始，然后改变一个或多个产生周期系统的细胞的特性时，就会发现缺陷状态。”首席研究员是印第安纳大学核理论中心主任。

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.