| The reactions $\\pi^- p \\to \\eta n$ and $\\gamma p \\to \\eta p$ are investigated within
a dynamical coupled-channels model of meson production reactions in the nucleon
resonance region.
The meson-baryon channels included are $\\pi N$, $\\eta N$, $\\pi \\Delta$, $\\sigma N$,
and $\\rho N$. The direct $\\eta$-photoproduction process is studied within a formalism based
on a chiral constituent quark model approach, complemented with a one-gluon-exchange
mechanism,
to take into account the breakdown of the $SU(6)\\otimes O(3)$ symmetry.
In the models search, the following known nucleon resonances are embodied:
$S_{11}(1535)$, $S_{11}(1650)$, $P_{11}(1440)$, $P_{11}(1710)$, $P_{13}(1720)$,
$D_{13}(1520)$, $D_{13}(1700)$, $D_{15}(1675)$, and $F_{15}(1680)$.
Data for the $\\pi^{-}p \\to \\eta n$ reaction from threshold up to a total center-of-mass
energy of $W ~\\approx$ 2 GeV are satisfactorily reproduced.
For the photoproduction channel, two additional higher mass known resonances,
$P_{13}(1900)$ and $F_{15}(2000)$, are also considered.
However, reproducing the data for $\\gamma p \\to \\eta p$ requires, within our approach, two new
nucleon resonances, for which we extract mass and width. |
