Speaker
Description
Photoproduction of $\eta$ and $\eta'$ on the nucleons was analyzed
within a new version of the $\eta$MAID model.
The model includes 23 nucleon resonances in the $s$ channel and $t$-channel
exchange of vector and axial-vector mesons with Regge cuts.
Parameters of the resonances were obtained from a fit to the new experimental data
of the A2 Collaboration and available data from CBELSA/TAPS, CLAS,
and GRAAL Collaborations for $\eta$ and $\eta'$ photoproduction on protons and
neutrons.
Dominant role of $1/2^-$ resonances is discussed.
The total cross section for the $\gamma p \to \eta p$ reaction demonstrates
a cusp at the energy W$\sim$1.9~GeV.
The cusp is explained as a threshold effect due to the opening $\eta' p$ decay
channel of the $N(1895)1/2^-$ resonance.
The model well describes both differential cross sections and polarisation
observables for photoproduction of $\eta$ and $\eta'$ on the nucleons
at photon beam energies from the threshold upto 8~GeV.
The model does not require additional contributions from exotic resonances to
explane a narrow stucture observed in $\gamma n \to \eta n$ reaction at
W$\sim$1.67~GeV.
