Unitary model for meson-nucleon scattering

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 $\pi N,$ $\pi \pi N,$ $\eta N,$ and $K\Lambda$ in the energy range $m_N{+m}_{\pi }<~\sqrt{s}<~1.9$ 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 $\pi N$–partial-wave analysis and the details of the Lagrangians and form factors used are discussed.