Search

The reaction gamma p -> K-S(0)Sigma(+) is studied in the photon energy range from threshold. Linearly polarised photon beams from coherent bremsstrahlung enabled the first measurement of photon beam asymmetries in this reaction up to E-gamma = 1650 MeV. In addition, the recoil hyperon polarisation was determined through the asymmetry in the weak decay Sigma(+) -> p pi(0) up to E-gamma = 2250 MeV. The data are compared to partial wave analyses, and the possible impact on the interpretation of a recently observed prominent structure in the cross section near the K* thresholds is discussed. (C) 2014 The Authors. Published by Elsevier B.V.

The reaction gamma p -> K-S(0)Sigma(+) is studied in the photon energy range from threshold. Linearly polarised photon beams from coherent bremsstrahlung enabled the first measurement of photon beam asymmetries in this reaction up to E-gamma = 1650 MeV. In addition, the recoil hyperon polarisation was determined through the asymmetry in the weak decay Sigma(+) -> p pi(0) up to E-gamma = 2250 MeV. The data are compared to partial wave analyses, and the possible impact on the interpretation of a recently observed prominent structure in the cross section near the K* thresholds is discussed. (C) 2014 The Authors. Published by Elsevier B.V.

Compton scattering off the proton in the third resonance region is analyzed for the first time, owing to the full combined analysis of pion- and photo-induced reactions in a coupled-channel effective Lagrangian model with K-matrix approximation. Two isospin $I=3/2$ resonances $D_{33}(1700)$ and $F_{35}(1930)$ are found to be essential in the range of 1.6 - 1.8 GeV. The recent beam asymmetry data of Compton scattering from the GRAAL facility are used to determine the helicity couplings of these resonances, and strong constraints are coming also from $\pi N$ and $K\Sigma$ photoproduction data. The possible spin and parity of new narrow resonances is discussed., Comment: 7 pages, 2 figs, 2 tabs, publish version

Precise helicity-dependent cross sections and the double-polarization observable E were measured for η photoproduction from quasifree protons and neutrons bound in the deuteron. The η→2γ and η→3π0→6γ decay modes were used to optimize the statistical quality of the data and to estimate systematic uncertainties. The measurement used the A2 detector setup at the tagged photon beam of the electron accelerator MAMI in Mainz. A longitudinally polarized deuterated butanol target was used in combination with a circularly polarized photon beam from bremsstrahlung of a longitudinally polarized electron beam. The reaction products were detected with the electromagnetic calorimeters Crystal Ball and TAPS, which covered 98% of the full solid angle. The results show that the narrow structure observed earlier in the unpolarized excitation function of η photoproduction off the neutron appears only in reactions with antiparallel photon and nucleon spin (σ1/2). It is absent for reactions with parallel spin orientation (σ3/2) and thus very probably related to partial waves with total spin 1/2. The behavior of the angular distributions of the helicity-dependent cross sections was analyzed by fitting them withLegendre polynomials. The results are in good agreement with a model from the Bonn-Gatchina group, which uses an interference of P11 and S11 partial waves to explain the narrow structure.

Photon beam asymmetry $\Sigma$ measurements for $\omega$ photoproduction in the reaction $\vec{\gamma} p \to \omega p$ are reported for photon energies from 1.152 to 1.876 GeV. Data were taken using a linearly-polarized tagged photon beam, a cryogenic hydrogen target, and the CLAS spectrometer in Hall B at Jefferson Lab. The measurements obtained markedly increase the size of the database for this observable, extend coverage to higher energies, and resolve discrepancies in previously published data. Comparisons of these new results with predictions from a chiral-quark-based model and from a dynamical coupled-channels model indicate the importance of interferences between $t$-channel meson exchange and $s$- and $u$-channel contributions, underscoring sensitivity to the nucleon resonances included in those descriptions. Comparisons with the Bonn-Gatchina partial-wave analysis indicate the $\Sigma$ data reported here help to fix the magnitudes of the interference terms between the leading amplitudes in that calculation (Pomeron exchange and the resonant portion of the $J^P=3/2^+$ partial wave), as well as the resonant portions of the smaller partial waves with $J^P$= $1/2^-$, $3/2^-$, and $5/2^+$., Comment: 10 pages, 3 figures

72 1024x768 Normal 0 false false false The assumption of cylindrical symmetry in radiotherapy accelerator models can pose a challenge for precise Monte Carlo modeling. This assumption makes it difficult to account for measured asymmetries in clinical dose distributions. We have performed a sensitivity study examining the effect of varying symmetric and asymmetric beam and geometric parameters of a Monte Carlo model for a Siemens PRIMUS accelerator. The accelerator and dose output were simulated using modified versions of BEAMnrc and DOSXYZnrc that allow lateral offsets of accelerator components and lateral and angular offsets for the incident electron beam. Dose distributions were studied for 40 × 40 cm2 fields. The resulting dose distributions were analyzed for changes in flatness, symmetry, and off-axis ratio (OAR). The electron beam parameters having the greatest effect on the resulting dose distributions were found to be electron energy and angle of incidence, as high as 5% for a 0.25° deflection. Electron spot size and lateral offset of the electron beam were found to have a smaller impact. Variations in photon target thickness were found to have a small effect. Small lateral offsets of the flattening filter caused significant variation to the OAR. In general, the greatest sensitivity to accelerator parameters could be observed for higher energies and off-axis ratios closer to the central axis. Lateral and angular offsets of beam and accelerator components have strong effects on dose distributions, and should be included in any high-accuracy beam model.

The polarization observable 15, a feature exclusive to the acoplanar kinematics of multi-meson final states produced via linearly polarized photons, has been measured for the first time. Results for the reaction (gamma) over barp -> p pi(0)eta are presented for incoming photon energies between 970 MeV and 1650 MeV along with the beam asymmetry I-c. The comparably large asymmetries demonstrate a high sensitivity of Is to the dynamics of the reaction. The sensitivity of these new polarization observables to the contributing partial waves is demonstrated by fits using the Bonn-Gatchina partial wave analysis. (C) 2010 Elsevier B.V. All rights reserved.

The polarization observable 15, a feature exclusive to the acoplanar kinematics of multi-meson final states produced via linearly polarized photons, has been measured for the first time. Results for the reaction (gamma) over barp -> p pi(0)eta are presented for incoming photon energies between 970 MeV and 1650 MeV along with the beam asymmetry I-c. The comparably large asymmetries demonstrate a high sensitivity of Is to the dynamics of the reaction. The sensitivity of these new polarization observables to the contributing partial waves is demonstrated by fits using the Bonn-Gatchina partial wave analysis. (C) 2010 Elsevier B.V. All rights reserved.

The photoproduction of eta-mesons off (12)C, (40)Ca, (93)Nb, and (nat)Pb nuclei has been measured with a tagged photon beam with energies between 0.6 and 2.2 GeV. The experiment was performed at the Bonn ELSA accelerator with the combined setup of the Crystal Barrel and TAPS calorimeters. It aimed at the in-medium properties of the S(11)(1535) nucleon resonance and the study of the absorption properties of nuclear matter for eta-mesons. Careful consideration was given to contributions from eta pi final states and secondary production mechanisms of eta-mesons, e.g. from inelastic pi N reactions of intermediate pions. The analysis of the mass number scaling shows that the nuclear absorption cross-section sigma(N eta) for eta-mesons is constant over a wide range of the eta momentum. The comparison of the excitation functions to data off the deuteron and to calculations in the framework of a BUU model show no unexplained in-medium modi. cations of the S(11)(1535).

The photoproduction of eta-mesons off (12)C, (40)Ca, (93)Nb, and (nat)Pb nuclei has been measured with a tagged photon beam with energies between 0.6 and 2.2 GeV. The experiment was performed at the Bonn ELSA accelerator with the combined setup of the Crystal Barrel and TAPS calorimeters. It aimed at the in-medium properties of the S(11)(1535) nucleon resonance and the study of the absorption properties of nuclear matter for eta-mesons. Careful consideration was given to contributions from eta pi final states and secondary production mechanisms of eta-mesons, e.g. from inelastic pi N reactions of intermediate pions. The analysis of the mass number scaling shows that the nuclear absorption cross-section sigma(N eta) for eta-mesons is constant over a wide range of the eta momentum. The comparison of the excitation functions to data off the deuteron and to calculations in the framework of a BUU model show no unexplained in-medium modi. cations of the S(11)(1535).

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.

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.

Hyperon production off the proton in the K-0 Sigma(+) channel has been studied at the tagged-photon beam facility at the ELSA electron accelerator in Bonn. This experiment was part of a series of neutral meson production experiments on various targets. For this purpose, the Crystal Barrel and TAPS photon spectrometers have been combined to provide a 4 pi detector for multi-neutral-particle final states. A high-quality excitation function, recoil polarizations, and angular distributions from threshold up to 2.3GeV center-of-mass energy were obtained. The results are compared with predictions of recent coupled-channel calculations within the K -matrix formalism and are interpreted by the partial-wave analysis within the Bonn-Gatchina model.

Hyperon production off the proton in the K-0 Sigma(+) channel has been studied at the tagged-photon beam facility at the ELSA electron accelerator in Bonn. This experiment was part of a series of neutral meson production experiments on various targets. For this purpose, the Crystal Barrel and TAPS photon spectrometers have been combined to provide a 4 pi detector for multi-neutral-particle final states. A high-quality excitation function, recoil polarizations, and angular distributions from threshold up to 2.3GeV center-of-mass energy were obtained. The results are compared with predictions of recent coupled-channel calculations within the K -matrix formalism and are interpreted by the partial-wave analysis within the Bonn-Gatchina model.

The reaction gamma p -> K-S(0)Sigma(+) is studied in the photon energy range from threshold. Linearly polarised photon beams from coherent bremsstrahlung enabled the first measurement of photon beam asymmetries in this reaction up to E-gamma = 1650 MeV. In addition, the recoil hyperon polarisation was determined through the asymmetry in the weak decay Sigma(+) -> p pi(0) up to E-gamma = 2250 MeV. The data are compared to partial wave analyses, and the possible impact on the interpretation of a recently observed prominent structure in the cross section near the K* thresholds is discussed. (C) 2014 The Authors. Published by Elsevier B.V.

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.

Quasi-free photoproduction of eta'-mesons off nucleons bound in the deuteron has been measured with the combined Crystal Barrel - TAPS detector. The experiment was done at a tagged photon beam of the ELSA electron accelerator in Bonn for incident photon energies from the production threshold up to 2.5 GeV. The eta'-mesons have been detected in coincidence with recoil protons and recoil neutrons. The quasi-free proton data are in good agreement with the results for free protons, indicating that nuclear effects have no significant impact. The coincidence with recoil neutrons provides the first data for the gamma n -> n eta' reaction. In addition, also first estimates for coherent eta'-production off the deuteron have been obtained. In agreement with model predictions, the total cross-section for this channel is found to be very small, at most at the level of a few nb. The data are compared to model calculations taking into account contributions from nucleon resonances and t-channel exchanges.

Quasi-free photoproduction of eta'-mesons off nucleons bound in the deuteron has been measured with the combined Crystal Barrel - TAPS detector. The experiment was done at a tagged photon beam of the ELSA electron accelerator in Bonn for incident photon energies from the production threshold up to 2.5 GeV. The eta'-mesons have been detected in coincidence with recoil protons and recoil neutrons. The quasi-free proton data are in good agreement with the results for free protons, indicating that nuclear effects have no significant impact. The coincidence with recoil neutrons provides the first data for the gamma n -> n eta' reaction. In addition, also first estimates for coherent eta'-production off the deuteron have been obtained. In agreement with model predictions, the total cross-section for this channel is found to be very small, at most at the level of a few nb. The data are compared to model calculations taking into account contributions from nucleon resonances and t-channel exchanges.

Quasi-free photoproduction of eta'-mesons off nucleons bound in the deuteron has been measured with the combined Crystal Barrel - TAPS detector. The experiment was done at a tagged photon beam of the ELSA electron accelerator in Bonn for incident photon energies from the production threshold up to 2.5 GeV. The eta'-mesons have been detected in coincidence with recoil protons and recoil neutrons. The quasi-free proton data are in good agreement with the results for free protons, indicating that nuclear effects have no significant impact. The coincidence with recoil neutrons provides the first data for the gamma n -> n eta' reaction. In addition, also first estimates for coherent eta'-production off the deuteron have been obtained. In agreement with model predictions, the total cross-section for this channel is found to be very small, at most at the level of a few nb. The data are compared to model calculations taking into account contributions from nucleon resonances and t-channel exchanges.

The polarization observable 15, a feature exclusive to the acoplanar kinematics of multi-meson final states produced via linearly polarized photons, has been measured for the first time. Results for the reaction (gamma) over barp -> p pi(0)eta are presented for incoming photon energies between 970 MeV and 1650 MeV along with the beam asymmetry I-c. The comparably large asymmetries demonstrate a high sensitivity of Is to the dynamics of the reaction. The sensitivity of these new polarization observables to the contributing partial waves is demonstrated by fits using the Bonn-Gatchina partial wave analysis. (C) 2010 Elsevier B.V. All rights reserved.

The resonance spectrum of the nucleon gives direct information on the dynamics and interactions of its constituents. This offers an important challenge to the theoretical models of nucleon structure, including the emerging Lattice QCD predictions, conformal field theories and more phenomenological, QCD-based approaches. Although the various models predict different features for the excitation spectra, the experimental information is currently of too poor quality to differentiate between these models. Pion photoproduction from the nucleon is a powerful probe of the spectrum as most resonances are expected to couple to the pion decay channel. However, cross-sections alone are not sensitive enough to allow identification of the underlying excitation spectrum, as the resonances have energy widths larger than their separations. A major world effort is underway to additionally measure polarisation observables in the production process. For a model-independent analysis a “complete” set of single- and doublepolarisation observables needs to be measured in experiments involving polarised beams, targets and a means of determining recoil nucleon polarisation. In particular, the beam asymmetry is a critical observable for the constraint of partial wave analyses (PWA) used to extract the nucleon excitation spectrum from the data. Almost all of the available world data on the beam asymmetry has been taken on the proton, with the neutron dataset sparse, containing only three experiments at fixed angles and in a limited photon energy range. The lack of extensive data on the neutron is a major deficiency, as different resonances have very different electromagnetic couplings to the proton and neutron. As a result, the data from the two targets will have very different relative contributions from, and sensitivities to, the spectrum of nucleon resonances. Moreover, neutron data is essential for the separation of the isoscalar and isovector components of the reaction amplitudes. This thesis presents a very high statistics measurement of the photon beam asymmetry on the neutron with close-to-complete angular coverage and a wide range of invariant mass (1610 – 2320 MeV) extending over the third resonance region, where the excitation spectrum is particularly ill defined. The experiment was conducted at the Thomas Jefferson National Accelerator Facility (JLab) using a tagged, linearly polarised photon beam, a liquid deuterium target and the CEBAF Large Acceptance Spectrometer (CLAS). The quality and quantity of the data has allowed an invariantmass resolution of 10 MeV and an angular resolution of 0.1 in the cosine of the centre-of-mass pion production angle, θ. Good agreement is evident in the regions where there is kinematic overlap with sparse previous data. Comparison of the new data is made with the two main partial wave analyses, SAID andMAID. Significant discrepancy is observed at backward θ with SAID (across most of the energy range) and MAID (up to ∼ 1750 MeV) and also below ∼ 35◦ in θ with both analyses. This extensive new dataset will help significantly to constrain partial wave analyses and will be a crucial part of the current world effort to use meson photoproduction to tackle long-standing uncertainties in the fundamental excitation spectrum of the nucleon. As a first step towards this the refitting of the SAID partial wave analysis incorporating the new data was carried out and shows very significant changes in the properties of the magnetic P11, P13, D13, D35, F15, G17 and G19 partial waves.

Total and differential cross sections for eta and eta(')photoproduction off the proton have been determined with the CBELSA/TAPS detector for photon energies between 0.85 and 2.55 GeV. The eta mesons are detected in their two neutral decay modes, eta ->gamma gamma and eta -> 3 pi(0)-> 6 gamma, and for the first time, cover the full angular range in cos theta(c.m.) of the eta meson. These new eta photoproduction data are consistent with the earlier CB-ELSA results. The eta(') mesons are observed in their neutral decay to pi(0)pi(0)eta -> 6 gamma and also extend the coverage in angular range.

Total and differential cross sections for eta and eta(')photoproduction off the proton have been determined with the CBELSA/TAPS detector for photon energies between 0.85 and 2.55 GeV. The eta mesons are detected in their two neutral decay modes, eta ->gamma gamma and eta -> 3 pi(0)-> 6 gamma, and for the first time, cover the full angular range in cos theta(c.m.) of the eta meson. These new eta photoproduction data are consistent with the earlier CB-ELSA results. The eta(') mesons are observed in their neutral decay to pi(0)pi(0)eta -> 6 gamma and also extend the coverage in angular range.

Total and differential cross sections for eta and eta(')photoproduction off the proton have been determined with the CBELSA/TAPS detector for photon energies between 0.85 and 2.55 GeV. The eta mesons are detected in their two neutral decay modes, eta ->gamma gamma and eta -> 3 pi(0)-> 6 gamma, and for the first time, cover the full angular range in cos theta(c.m.) of the eta meson. These new eta photoproduction data are consistent with the earlier CB-ELSA results. The eta(') mesons are observed in their neutral decay to pi(0)pi(0)eta -> 6 gamma and also extend the coverage in angular range.

We investigate photoproduction of. mesons off protons and neutrons within a coupled-channels effective-Lagrangian method that is based on the K-matrix approach. The two-body final channels included are pi N, eta N, phi N, rho N, gamma N, K Lambda, and K Sigma. Nonresonant meson-baryon interactions are included in the model via nucleon intermediate states in the s and u channels and meson exchanges in the t-channel amplitude and the u-channel resonances. The nucleon resonances S(11)(1535), S(11)(1650), S(31)(1620), P(11)(1440), P(11)(1710), P(13)(1720), P(33)( 1232), P(33)(1600), D(13)(1520), D(13)(1700), and D(33)(1700) are included explicitly in calculations. Our model describes simultaneously the available data as well on total and differential cross sections as on beam and target asymmetries. This holds for the gamma p -> eta p reaction for photon energies ranging from very close to threshold to up to 3 GeV. The polarization observables show strong sensitivity to resonances that otherwise contribute only weakly to the total cross section. It is found that the pronounced bumplike structure seen in the excitation function of the gamma n -> eta n cross section at gamma energies around 1 GeV can be explained by the interference effects of S(11), P(11), and P(13) resonance contributions.

We investigate photoproduction of. mesons off protons and neutrons within a coupled-channels effective-Lagrangian method that is based on the K-matrix approach. The two-body final channels included are pi N, eta N, phi N, rho N, gamma N, K Lambda, and K Sigma. Nonresonant meson-baryon interactions are included in the model via nucleon intermediate states in the s and u channels and meson exchanges in the t-channel amplitude and the u-channel resonances. The nucleon resonances S(11)(1535), S(11)(1650), S(31)(1620), P(11)(1440), P(11)(1710), P(13)(1720), P(33)( 1232), P(33)(1600), D(13)(1520), D(13)(1700), and D(33)(1700) are included explicitly in calculations. Our model describes simultaneously the available data as well on total and differential cross sections as on beam and target asymmetries. This holds for the gamma p -> eta p reaction for photon energies ranging from very close to threshold to up to 3 GeV. The polarization observables show strong sensitivity to resonances that otherwise contribute only weakly to the total cross section. It is found that the pronounced bumplike structure seen in the excitation function of the gamma n -> eta n cross section at gamma energies around 1 GeV can be explained by the interference effects of S(11), P(11), and P(13) resonance contributions.

We investigate photoproduction of. mesons off protons and neutrons within a coupled-channels effective-Lagrangian method that is based on the K-matrix approach. The two-body final channels included are pi N, eta N, phi N, rho N, gamma N, K Lambda, and K Sigma. Nonresonant meson-baryon interactions are included in the model via nucleon intermediate states in the s and u channels and meson exchanges in the t-channel amplitude and the u-channel resonances. The nucleon resonances S(11)(1535), S(11)(1650), S(31)(1620), P(11)(1440), P(11)(1710), P(13)(1720), P(33)( 1232), P(33)(1600), D(13)(1520), D(13)(1700), and D(33)(1700) are included explicitly in calculations. Our model describes simultaneously the available data as well on total and differential cross sections as on beam and target asymmetries. This holds for the gamma p -> eta p reaction for photon energies ranging from very close to threshold to up to 3 GeV. The polarization observables show strong sensitivity to resonances that otherwise contribute only weakly to the total cross section. It is found that the pronounced bumplike structure seen in the excitation function of the gamma n -> eta n cross section at gamma energies around 1 GeV can be explained by the interference effects of S(11), P(11), and P(13) resonance contributions.

The photoproduction of eta-mesons off (12)C, (40)Ca, (93)Nb, and (nat)Pb nuclei has been measured with a tagged photon beam with energies between 0.6 and 2.2 GeV. The experiment was performed at the Bonn ELSA accelerator with the combined setup of the Crystal Barrel and TAPS calorimeters. It aimed at the in-medium properties of the S(11)(1535) nucleon resonance and the study of the absorption properties of nuclear matter for eta-mesons. Careful consideration was given to contributions from eta pi final states and secondary production mechanisms of eta-mesons, e.g. from inelastic pi N reactions of intermediate pions. The analysis of the mass number scaling shows that the nuclear absorption cross-section sigma(N eta) for eta-mesons is constant over a wide range of the eta momentum. The comparison of the excitation functions to data off the deuteron and to calculations in the framework of a BUU model show no unexplained in-medium modi. cations of the S(11)(1535).

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.

Precise data for quasi-free photoproduction of η-mesons off the deuteron have been measured at the Bonn ELSA accelerator with the combined Crystal Barrel/TAPS detector for incident photon energies up to 2.5GeV. The η-mesons have been detected in coincidence with recoil protons and neutrons. Possible nuclear effects like Fermi motion and re-scattering can be studied via a comparison of the quasi-free reaction off the bound proton to η-production off the free proton. No significant effects beyond the folding of the free cross-section with the momentum distribution of the bound protons have been found. These Fermi motion effects can be removed by an analysis using the invariant mass of the η-nucleon pairs reconstructed from the final-state four-momenta of the particles. The total cross-section for quasi-free η-photoproduction off the neutron reveals even without correction for Fermi motion a pronounced bump-like structure around 1GeV of incident photon energy, which is not observed for the proton. This structure is even narrower in the invariant-mass spectrum of the η-neutron pairs. Position and width of the peak in the invariant-mass spectrum are W ≈ 1665 MeV and FWHM Γ ≈ 25 MeV. The data are compared to the results of different models.

Hyperon production off the proton in the K-0 Sigma(+) channel has been studied at the tagged-photon beam facility at the ELSA electron accelerator in Bonn. This experiment was part of a series of neutral meson production experiments on various targets. For this purpose, the Crystal Barrel and TAPS photon spectrometers have been combined to provide a 4 pi detector for multi-neutral-particle final states. A high-quality excitation function, recoil polarizations, and angular distributions from threshold up to 2.3GeV center-of-mass energy were obtained. The results are compared with predictions of recent coupled-channel calculations within the K -matrix formalism and are interpreted by the partial-wave analysis within the Bonn-Gatchina model.

The analysis of the gamma p ->eta pi(0)p reaction has been performed using data from the GRAAL experiment. The total and differential cross sections and the beam asymmetry have been obtained from threshold up to 1.5 GeV of beam energy. The two resonances S-11(1535) and Delta(1700) are expected to be excited in the intermediate states of this reaction. The results are used to test predictions based on the assumption that both resonances are dynamically generated from the meson-baryon interaction provided by chiral Lagrangians. The term involving the Delta(1700) excitation, followed by the decay into eta Delta(1232), is found to be dominant.

The charged pion production reactions d(gamma,pi+n), d(gamma,pi-p), HD(gamma,pi+n)X were studied using linearly polarized gamma-rays with energies in the range from 260 MeV to 370 MeV at the Laser Electron Gamma Source (LEGS). A solid HD target was used in this experiment for the first time. The beam asymmetry data for the d(gamma,pi-p) reaction significantly add to the previously available data. This gives new input to multipole analysis of pion production. A slight deviation from the beam asymmetry predicted for the free neutron is observed. The cross sections in the d(gamma,pi-p) channel agree with previous measurements. Ph. D.