The s-wave meson-baryon scattering is analyzed for the strangeness $S=0\mathrm{}$ sector in a Bethe-Salpeter coupled channel formalism incorporating chiral symmetry. Four channels have been considered: $\pi N,\eta N,K\Lambda ,K\Sigma .$ The needed two-particle irreducible matrix amplitude is taken from lowest order chiral perturbation theory in a relativistic formalism and low energy constants are fitted to the elastic $\pi N$ phase shifts and the ${\pi }^{-}\overrightarrow{p}\eta n$ and ${\pi }^{-}\overrightarrow{p}{K}^0\Lambda$ cross section data. The position of the complex poles in the second Riemann sheet of the scattering amplitude determines masses and widths of the $S_{11}-N\left(1535\right)\mathrm{}$ and $-N\left(1650\right)\mathrm{}$ resonances, in reasonable agreement with experiment. A good overall description of data, from $\pi N$ threshold up to 2 GeV, is achieved, keeping in mind that the two-pion production channel has not been included.

• Received 27 April 2001

DOI:https://doi.org/10.1103/PhysRevD.64.116008