Meson-Baryon Scattering from Threshold to the Second Resonance Region

• Applicant: Professor Dr. Michael Ulrich Döring
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2007 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 42185146

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.

• DFG Programme: Research Grants