Meson-Baryon Scattering from Threshold to the Second Resonance Region

非微扰区域中的强相互作用仍然是标准模型中最不被理解的部分之一。特别是，夸克如何被限制在物理上可观察到的状态，即介子和重子，目前还不清楚。目前，为了更好地理解激发重子(共振)及其衰变，人们在理论和实验上都做出了努力。在最初几个月的研究中，我们进一步发展了描述介子-重子散射的理论模型。所谓的Jülich模型是一种基于介子交换的解析么正模型。Jülich模型的振幅是在遵守手征约束的拉格朗日量的场论方法下得到的。在各种分波中以高精度描述数据。我们发现，有了这些成分，再加上对分析性质和三个主体切割的彻底处理，可靠和精确地提取极点位置和残留物成为可能。我们还表明，分解为极点和非极点部分是模型相关的，可靠的共振参数是由极点位置和剩余部分给出的，而不是修饰顶点或Breit-Wigner参数。我们的研究结果最近已经送来出版了。根据我们在调查中获得的见解和新开发的方法，我们计划扩大这项工作。我们的下一个目标是详细研究对πNππN反应很重要的三体奇点；现在有大量关于这些反应的最新数据。此外，我们计划在低能限下将Jülich模型的振幅与手征微扰理论相匹配。额外的限制将来自在高能下与Regge理论的匹配，以及包括高达2GeV的能量的额外通道。

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.