Meson-Baryon Scattering from Threshold to the Second Resonance Region

非摄动状态下的强相互作用仍然是标准模型中最不为人所知的部分之一。特别是，目前还不清楚夸克是如何被限制在被称为介子和重子的物理可观察状态中的。目前，理论和实验都在努力更好地理解激发态重子（共振）及其衰变。在我们研究的头几个月里，我们进一步发展了一个描述介子-重子散射的理论模型。所谓j<s:1> lich模型是基于介子交换的解析一元模型。j<s:1>利希模型的振幅是由拉格朗日量服从手性约束的场理论方法推导出来的。在各种分波中，数据被描述得精度很高。我们发现，有了这些成分，再加上对解析性质和三体切割的彻底处理，可靠而精确地提取极点位置和残馀成为可能。我们还证明了极和非极部分的分解是一个在文献中广泛使用的概念，它是模型依赖的，可靠的共振参数是由极位置和残基给出的，而不是由修饰顶点或Breit-Wigner参数化给出的。我们的研究结果最近已寄去发表。根据我们在调查中获得的见解和新开发的方法，我们计划扩展这项工作。我们的下一个目标是详细研究三体奇点对πN的重要性ππN反应；现在有大量关于这些反应的最新数据。此外，我们计划在低能极限下将j<s:1> lich模型的振幅与手性微扰理论相匹配。额外的限制将来自于在高能量下与Regge理论的匹配，以及包含高达2 GeV能量的额外通道。

Strong interactions in the non-perturbative regime are still one of the least understood parts of the Standard Model. In particular it is not clear how quarks get confined into physically observable states called mesons and baryons. Currently, theoretical and experimental efforts are made to better understand excited baryons (resonances) and their decays. During the first months of our investigations, we have further developed a theoretical model of the description of meson-baryon scattering. The so-called Jülich model is an analytic unitary model based on meson exchange. The amplitudes of the Jülich model are derived within a field theoretical approach from Lagrangians obeying chiral constraints. Data are described to a high precision in the various partial waves. We found that with these ingredients, in combination with a thorough treatment of the analytic properties and three body cuts, a reliable and precise extraction of pole positions and residues becomes possible. We have also shown that the decomposition into pole and non-pole part, a widely used concept in the literature, is model dependent and that reliable resonance parameters are given by pole positions and residues rather than dressed vertices or Breit-Wigner parameterizations. Our results have been sent for publication recently. Based on the insights obtained during our investigation and the newly developed methods, we plan to extend the work. Our next target is the detailed study of three-body singularities important for the πN  ππN reaction; there is a large amount of recent data available now for these reactions. Moreover, we plan to match the amplitudes of the Jülich model to chiral perturbation theory in the low energy limit. Additional constraints will come from a matching to Regge theory at high energy and the inclusion of additional channels up to an energy of 2 GeV.