Mixing of pseudoscalar-baryon and vector-baryon in the $J^P=1/2^{-}$ sector and the $N^{\ast }$(1535) and $N^{\ast }$(1650) resonances

Abstract

We study the meson-baryon interaction with $J^P=1/2^{-}$ using the hidden-gauge Lagrangians and mixing pseudoscalar meson-baryon with the vector meson-baryon states in a coupled channels scheme with $\pi N$, $\eta N$, $K\Lambda$, $K\Sigma$, $\rho N$ and $\pi \Delta$ (d-wave). We fit the subtraction constants of each channel to the $S_{11}$ partial wave amplitude of the $\pi N$ scattering data extracted from experimental data. We find two poles that we associate to the $N^{\ast }(1535)$ and the $N^{\ast }(1650)$ resonances and show that the subtraction constants are all negative and of natural size. We calculate the branching ratios for the different channels of each resonance and we find a good agreement with the experimental data. The cross section for the ${\pi }^{-}p\to \eta n$ scattering is also evaluated and compared with experiment.