Meson Production on the Nucleon in the Giessen K-Matrix Approach

Meson production on the proton is described in a coupled channels K-matrix approach. Both hadronic and photonic scenarios are taken into account on the same theoretical footing. At tree-level the Born amplitudes are obtained from an effective Lagrangian with phenomenologically adjustable coupling constants. The spectral distributions, resonances and their width and the background contributions are obtained within the same approach, thus accounting properly for interference effects. Applications to omega- and associated strangeness production on the proton are discussed.Comment: 11 pages, 6 Figures, Proc. Int. Workshop NSTAR 2005 at Tallahassee, Fl., Oct. 200

Spin-5/2 resonance contributions to the pion-induced reactions for energies s⩽\sqrt{s}\leqslant2.0 GeV

The spin-\ffh resonance effects are studied within the coupled channel effective Lagrangian model for baryon resonance analysis. We extend our previous hadronic calculations to incorporate the $D_{15}$, $F_{15}$, $D_{35}$, $F_{35}$ states. While the effect of the spin-\ffh resonances to the $\eta N$, $K \Lambda$, and $K \Sigma$ reactions are small, the contribution to the $\omega N$ is found to be important. The results for the 'conventional' and Pascalutsa-like spin-\ffh descriptions are discussed. \PACS{{11.80.-m},{13.75.Gx},{14.20.Gk},{13.30.Gk}}Comment: Eur. J Phys. A (in print

2π2\pi production in the Giessen coupled-channel model

We present a coupled-channel Lagrangian approach (GiM) to describe the $\pi N \to \pi N$, $2\pi N$ scattering in the resonance energy region. The $2\pi N$ production has been significantly improved by using the isobar approximation with $\sigma N$ and $\pi \Delta(1232)$ in the intermediate state. The three-body unitarity is maintained up to interference pattern between the isobar subchannels. The scattering amplitudes are obtained as a solution of the Bethe-Salpeter equation in the $K$ matrix approximation. As a first application we perform a partial wave analysis of the $\pi N \to \pi N$, $\pi^0\pi^0 N$ reactions in the Roper resonance region. We obtain $R_{\sigma N}(1440)=27^{+4}_{-9}$\,\% and $R_{\sigma N}(1440)=12^{+5}_{-3}$\,\% for the $\sigma N$ and $\pi \Delta$ decay branching ratios of $N^*(1440)$ respectively. The extracted $\pi N$ inelasticities and reaction amplitudes are consistent with the results from other groups.Comment: replaced with the published versio

Eta-meson production in the resonance energy region

We perform an updated coupled-channel analysis of eta-meson production including all recent photoproduction data on the proton. The dip observed in the differential cross sections at c.m. energies W=1.68 GeV is explained by destructive interference between the $S_{11}(1535)$ and $S_{11}(1560)$ states. The effect from $P_{11}(1710)$ is found to be small but still important to reproduce the correct shape of the differential cross section. For the $\pi^- N \to \eta N$ scattering we suggest a reaction mechanism in terms of the $S_{11}(1535)$, $S_{11}(1560)$, and $P_{11}(1710)$ states. Our conclusion on the importance of the $S_{11}(1535)$, $S_{11}(1560)$, and $P_{11}(1710)$ resonances in the eta-production reactions is in line with our previous results. No strong indication for a narrow state with a width of 15 MeV and the mass of 1680 MeV is found in the analysis. $\eta N$ scattering length is extracted and discussed.Comment: replaced with a published version, pole parameters and scattering lengths are adde

eta-photoproduction in the resonance energy region

The $\eta$ production in the nucleon resonance energy region is studied within the unitary coupled-channels effective Lagrangian approach of the Giessen model. We demonstrate that the second peak recently observed in the cross section of $\eta$ photoproduction on the neutron at $\sqrt{s}$=1.66 GeV can be explained in terms of coupled-channel effects due to $S_{11}(1650)$ and $P_{11}(1710)$ resonance excitations