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Bochum 1998 – scientific programme

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HK: Hadronen und Kerne

HK 20: Structure of Baryons, Mesons III, Theory

HK 20.1: Group Report

Monday, March 16, 1998, 17:00–17:30, H

Nucleon resonances in π N scattering — •O. Krehl1, C. Schütz1, J. Haidenbauer1, J.W. Durso2, and J. Speth11Institut f"ur Kernphysik, Forschungszentrum J"ulich GmbH, 52425 J"ulich — 2Physics Department, Mount Holyoke College, South Hadley, Ma 01075, USA

We present a coupled channel π NNN/π Δ meson exchange model for π N scattering which gives a good description of π N phase shifts and inelasticities up to π N c.m. energies of 1600 MeV.

Within this model we investigate the question whether the experimentally observed baryon resonances in this energy range contain a genuine three-quark contribution or whether they can be understood purely in terms of the underlying meson-baryon dynamics.

The rise of the P11 phase shifts in the energy region below the Roper resonance (N*(1440)) can be understood in elastic π N scattering without a genuine N* [1]. The coupling to the σ N and π Δ channels (as effective parameterization of ππ N states) accounts for the inelasticity in the P11 partial wave [2].

In the second part we concentrate on the S11-wave resonance N*(1535) which strongly couples to the η N channel. The influence of descriptions with and without three-quark state on the π N phase shifts and π N → η N total and differential cross sections are discussed.

[1] C. Schütz, J.W. Durso, K. Holinde and J. Speth, Phys. Rev. C 49 (1994) 2671.

[2] C. Schütz, J. Haidenbauer, J.W. Durso and J. Speth, submitted for publication

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