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The gamma + p -> K-0 + Sigma(+) photoproduction reaction is investigated in the energy region from threshold to E gamma = 2250 MeV. The differential cross section exhibits increasing forward-peaking with energy, but only up to the K* threshold. Beyond, it suddenly returns to a flat distribution with the forward cross section dropping by a factor of four. In the total cross section a pronounced structure is observed between the K*Lambda and K*Sigma thresholds. (C) 2012 Published by Elsevier B.V.

The reaction gamma p -> p pi(0)eta has been studied with the CBELSA detector at the tagged photon beam of the Bonn electron stretcher facility. The reaction shows contributions from Delta(+)(1232)eta, N(1535)(+) pi(0) and pa(0)(980) as intermediate states. A partial-wave analysis suggests that the reaction proceeds via formation of six Delta-resonances, Delta(1600)P-33, Delta(1920)P-33, Delta(1700)D-33, Delta(1940)D-33, Delta(1905)F-35, Delta(2360)D-33, and two nucleon resonances N(1880)P-11 and N(2200)P-13, for which pole positions and decay branching ratios are given.

Decays of baryon resonances in the second and the third resonance region into N pi(0)pi(0) are studied by photoproduction of two neutral pions off protons. Partial decay widths of N* and Delta* resonances decaying into Delta(1232)pi, N(pi pi)(S), N(1440)P-11 pi, and N(1520)D-13 pi are determined in a partial wave analysis of this data and of data from other reactions. Several partial decay widths were not known before. Interesting decay patterns are observed which are not even qualitatively reproduced by quark model calculations. In the second resonance region, decays into Delta(1232)pi dominate clearly. The N(pi pi)(S)-wave provides a significant contribution to the cross section, especially in the third resonance region. The P-13(1720) properties found here are at clear variance to PDG values.

Photoproduction of pi(0)-mesons was studied with the Crystal-Barrel detector at ELSA for incident energies from 300 MeV to 3 GeV. Differential cross-sections d sigma/d Omega, d sigma/dt, and the total cross-section are presented. For E (gamma)

Photoproduction off protons of the p pi(0)eta three-body final state was studied with the Crystal Barrel/TAPS detector, at the electron stretcher accelerator ELSA in Bonn, for incident energies from the pi(0)eta production threshold up to 2.5 GeV. Differential cross sections and the total cross sections are presented. The use of linearly polarized photons gives access to the polarization observables Sigma, I-s, and I-c, the latter two characterize beam asymmetries in case of three-body final states. Delta(1232)(eta), N(1535)1/2(-) pi, and pa(0)(980) are the dominant isobars contributing to the reaction. The partial wave analysis confirms the existence of some nucleon and Delta resonances, for which so far only fair evidence was reported. A large number of decay modes of known nucleon and Delta resonances is presented. It is shown that detailed investigations of decay branching ratios may provide a key to unravelling the structure of nucleon and Delta resonances.

Photoproduction off protons of the p pi(0)eta three-body final state was studied with the Crystal Barrel/TAPS detector, at the electron stretcher accelerator ELSA in Bonn, for incident energies from the pi(0)eta production threshold up to 2.5 GeV. Differential cross sections and the total cross sections are presented. The use of linearly polarized photons gives access to the polarization observables Sigma, I-s, and I-c, the latter two characterize beam asymmetries in case of three-body final states. Delta(1232)(eta), N(1535)1/2(-) pi, and pa(0)(980) are the dominant isobars contributing to the reaction. The partial wave analysis confirms the existence of some nucleon and Delta resonances, for which so far only fair evidence was reported. A large number of decay modes of known nucleon and Delta resonances is presented. It is shown that detailed investigations of decay branching ratios may provide a key to unravelling the structure of nucleon and Delta resonances.

In photoproduction experiments, a large number of final states yielding various resonance contributions are accessible. To extract resonance parameters via partial-wave analysis not only the measurement of differential cross-sections is necessary, but also the determination of polarization observables. At the electron accelerator ELSA (Bonn) the coherent bremsstrahlung method was used to generate a linearly polarized photon beam. Using the CBELSA/TAPS detector setup, the beam asymmetry Sigma in the reaction gamma p -> p pi(0) eta was determined as a function of various masses and angles for photon energies between 970MeV and 1650MeV.

The gamma + p -> K-0 + Sigma(+) photoproduction reaction is investigated in the energy region from threshold to E gamma = 2250 MeV. The differential cross section exhibits increasing forward-peaking with energy, but only up to the K* threshold. Beyond, it suddenly returns to a flat distribution with the forward cross section dropping by a factor of four. In the total cross section a pronounced structure is observed between the K*Lambda and K*Sigma thresholds. (C) 2012 Published by Elsevier B.V.

The reaction gamma p -> p pi(0)eta has been studied with the CBELSA detector at the tagged photon beam of the Bonn electron stretcher facility. The reaction shows contributions from Delta(+)(1232)eta, N(1535)(+) pi(0) and pa(0)(980) as intermediate states. A partial-wave analysis suggests that the reaction proceeds via formation of six Delta-resonances, Delta(1600)P-33, Delta(1920)P-33, Delta(1700)D-33, Delta(1940)D-33, Delta(1905)F-35, Delta(2360)D-33, and two nucleon resonances N(1880)P-11 and N(2200)P-13, for which pole positions and decay branching ratios are given.

In photoproduction experiments, a large number of final states yielding various resonance contributions are accessible. To extract resonance parameters via partial-wave analysis not only the measurement of differential cross-sections is necessary, but also the determination of polarization observables. At the electron accelerator ELSA (Bonn) the coherent bremsstrahlung method was used to generate a linearly polarized photon beam. Using the CBELSA/TAPS detector setup, the beam asymmetry Sigma in the reaction gamma p -> p pi(0) eta was determined as a function of various masses and angles for photon energies between 970MeV and 1650MeV.

Decays of baryon resonances in the second and the third resonance region into N pi(0)pi(0) are studied by photoproduction of two neutral pions off protons. Partial decay widths of N* and Delta* resonances decaying into Delta(1232)pi, N(pi pi)(S), N(1440)P-11 pi, and N(1520)D-13 pi are determined in a partial wave analysis of this data and of data from other reactions. Several partial decay widths were not known before. Interesting decay patterns are observed which are not even qualitatively reproduced by quark model calculations. In the second resonance region, decays into Delta(1232)pi dominate clearly. The N(pi pi)(S)-wave provides a significant contribution to the cross section, especially in the third resonance region. The P-13(1720) properties found here are at clear variance to PDG values.

Differential and total cross-sections for photoproduction of gamma proton to proton pi0 omega and gamma proton to Delta+ omega were determined from measurements of the CB-ELSA experiment, performed at the electron accelerator ELSA in Bonn. The measurements covered the photon energy range from the production threshold up to 3GeV.

The beam asymmetry, $\Sigma$, was measured at ELSA in the reaction $\vec \gamma p \to \eta p$ using linearly polarised tagged photon beams, produced by coherent bremsstrahlung off a diamond. The crystal was oriented to provide polarised photons in the energy range $E_\gamma = 800$ to 1400 MeV with the maximum polarisation of $P_\gamma = 49$ % obtained at 1305 MeV. Both dominant decay modes of the $\eta$ into two photons and $3\pi^0$ were used to extract the beam asymmetry from the azimuthal modulation of the cross section. The measurements cover the angular range $\Theta_\text{cm}\simeq 50$ -- 150 degrees. Large asymmetries up to 80 % are observed, in agreement with a previous measurement. The eta-MAID model and the Bonn--Gatchina partial wave analysis describe the measurements, but the required partial waves differ significantly., Comment: 8 pages, 8 figures, submitted to EPJA

Photoproduction of pi(0)-mesons was studied with the Crystal-Barrel detector at ELSA for incident energies from 300 MeV to 3 GeV. Differential cross-sections d sigma/d Omega, d sigma/dt, and the total cross-section are presented. For E (gamma)

Photoproduction of η -mesons was studied with the Crystal-Barrel detector at ELSA for photon energies in the range from 0.75 to 3GeV. Total and differential cross-sections are presented. The η mesons are detected in two decay modes, in η → 2γ and in η → 3π0 → 6γ . The cross-sections vary slowly as functions of energy and η production angle suggesting that only few resonances make significant contributions to the cross-section. For photon energies above 1.5GeV, the differential cross-sections show a strong forward peak due to meson exchanges in the t channel. A comparison of the η -photoproduction cross-sections with SAID and MAID as well as with a partial-wave analysis performed on our data in combination with other data sets shows good agreement. The Bonn-Gatchina partial-wave analysis suggests that the largest contribution to η photoproduction for energies below 3GeV proceeds via three resonances, the well-known N(1535)S 11 , via N(1720)P 13 , and a newly suggested N(2070)D 15 .

Properties of the Roper resonance, the first scalar excitation of the nucleon, are determined. Pole positions and residues of the $P_{11}$ partial wave are studied in a combined analysis of pion- and photo-induced reactions. We find the Roper pole at $\{(1371\pm7)-i(92\pm10)\}$ MeV and an elasticity of $0.61\pm 0.03$. The largest decay coupling is found for the $N\sigma$ ($\sigma=(\pi\pi)$-$S$-wave). The analysis is based on new data on $\gamma p\to p\pi^0\pi^0$ for photons in the energy range from the two-pion threshold to 820 MeV from TAPS at Mainz and from 0.4 to 1.3 GeV from Crystal Barrel at Bonn and includes further data from other experiments. The partial wave analysis excludes the possibility that the Roper resonance is split into two states with different partial decay widths., Comment: 14 pages, 6 figures

A coupled-channels analysis, based on the K-matrix approach, is presented for photo-induced kaon production. It is shown that channel coupling effects are large and should not be ignored. The importance of contact terms in the analysis, associated with short-range correlations, is pointed out. The extracted parameters are compared with SU(3) model predictions.

A coupled-channels analysis, based on the K-matrix approach, is presented for photo-induced kaon production. It is shown that channel coupling effects are large and should not be ignored. The importance of contact terms in the analysis, associated with short-range correlations, is pointed out. The extracted parameters are compared with SU(3) model predictions.