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HK: Physik der Hadronen und Kerne
HK 9: Theorie II
HK 9.2: Talk
Monday, March 22, 1999, 17:00–17:15, A
Extended couple channel model for π N scattering — •O. Krehl, S. Krewald, and J. Speth — Institut f"ur Kernphysik, Forschungszentrum J"ulich GmbH, 52425 J"ulich
We have extended the Jülich π N/π Δ / σ N/ η N coupled channel model [1] by including the coupling to the ρ N. The ρ N channel is treated as an effective ππ N channel and therefore completes the dominant ππ N channels (π Δ and σ N ) in our model.
Whithin this model we investigate the structure of the first nucleon resonances, especially the D13(1520) (which couples strongly to ρ N) and the P11(1440) (Roper) as the lowest exitations of the nucleon with negative and poitive parity respectively. To do so, it is cruical to iterate the potential – which is constructed by using an effective Lagrangian – up to infinite order, because only this method may eventually generate dynamical poles.
The ρ N channel improves the description of the π N phase shifts and inelasticities below energies of about 1800 MeV c.m. in detail but does not lead to additional dynamical poles. The coupling constants for this additional channel are fixed from other sources whereas the cutoffs are fixed by the π N phase shifts and the transition cross section π N → ρ N which we will discuss in detail.
[1] C. Schütz, J. Haidenbauer, J.W. Durso and J. Speth, Phys. Rev. C C 57 (1998) 1464