Unitary model for meson-nucleon scattering

Abstract

We extract nucleon resonance parameters from an effective Lagrangian model employing the $K$-matrix approximation. To this end we analyze simultaneously all available data for reactions involving the final states $\ensuremath{\pi}N,$ $\ensuremath{\pi}\ensuremath{\pi}N,$ $\ensuremath{\eta}N,$ and $K\ensuremath{\Lambda}$ in the energy range ${m}_{N}{+m}_{\ensuremath{\pi}}<~\sqrt{s}<~1.9$ GeV. The background contributions are generated consistently from the relevant Feynman amplitudes, which significantly reduces the number of free parameters. The sensitivity of the parameters upon the $\ensuremath{\pi}N$--partial-wave analysis and the details of the Lagrangians and form factors used are discussed.