Combined study of $\gamma p \to \eta p$ and $pi^- p \to \eta n$ in a chiral constituent quark approach

Within a chiral constituent quark model approach, $\ensuremath{\eta}$-meson production on the proton via electromagnetic and hadron probes is studied. With few parameters, the differential cross section and polarized beam asymmetry for $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\eta}p$ and differential cross section for ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}\ensuremath{\eta}n$ processes are calculated and successfully compared with the data in the center-of-mass energy range from threshold up to 2 GeV. The five known resonances ${S}_{11}(1535)$, ${S}_{11}(1650)$, ${P}_{13}(1720)$, ${D}_{13}(1520)$, and ${F}_{15}(1680)$ are found to be dominant in the reaction mechanisms in both channels. Possible roles played by new resonances are also investigated; and in the photoproduction channel, significant contribution from ${S}_{11}$ and ${D}_{15}$ resonances, with masses around 1715 and 2090 MeV, respectively, are deduced. For the so-called missing resonances, no evidence is found within the investigated reactions. The helicity amplitudes and decay widths of ${N}^{*}\ensuremath{\rightarrow}\ensuremath{\pi}N$, $\ensuremath{\eta}N$ are also presented and found to be consistent with the Particle Data Group values.