The Structure of Baryon Resonances in piN Scattering

We present a coupled channel model for pi N scattering, based on meson and baryon exchange processes. The inclusion of the reaction channels pi N, pi Delta sigma N and eta N leads to a good description of pi N phase shifts and inelasticities up to c.m. energies of 1600 MeV. The coupling between the channels pi N, pi Delta and sigma N turns out to be large in the P(11) and the N*(1440) (Roper) resonance call be explained solely by meson-baryon dynamics, i.e. without the inclusion of a genuine N*(1440) resonance. For the investigation of the N* (1535) resonance, the model is extended by including the eta N reaction channel. A genuine N*(1535) resonance is needed for a quantitative description of the pi N phase shift in the S(11), but the background from meson and baryon exchanges is large and cannot be neglected.