Search

The reaction γ p → pπ0η has been studied with the CBELSA detector at the tagged photon beam of the Bonn electron stretcher facility. The reaction shows contributions from Δ+(1232)η , N(1535)+π0 and pa 0(980) as intermediate states. A partial-wave analysis suggests that the reaction proceeds via formation of six Δ -resonances, Δ(1600) P 33 , Δ(1920) P 33 , Δ(1700) D 33 , Δ(1940) D 33 , Δ(1905) F 35 , Δ(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. [ABSTRACT FROM AUTHOR]

Abstract: Properties of the Roper resonance, the first scalar excitation of the nucleon, are determined. Pole positions and residues of the partial wave are studied in a combined analysis of pion- and photo-induced reactions. We find the Roper pole at and an elasticity of . The largest decay coupling is found for the Nσ (-S-wave). The analysis is based on new data on 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. [Copyright &y& Elsevier]

Abstract: Decays of baryon resonances in the second and the third resonance region into are studied by photoproduction of two neutral pions off protons. Partial decay widths of and resonances decaying into , , , and 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 dominate clearly. The -wave provides a significant contribution to the cross section, especially in the third resonance region. The (1720) properties found here are at clear variance to PDG values. [Copyright &y& Elsevier]

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 . [ABSTRACT FROM AUTHOR]

Differential and total cross-sections for photoproduction of γp→ pπ 0 ω and γp→ Δ + ω 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. [ABSTRACT FROM AUTHOR]

Photoproduction of π0-mesons was studied with the Crystal-Barrel detector at ELSA for incident energies from 300MeV to 3GeV. Differential cross-sections dσ/ dΩ, dσ/ dt, and the total cross-section are presented. For E γ < 3GeV, the angular distributions agree well with the SAID parametrization. At photon energies above 1.5GeV, a strong forward peaking indicates t-channel exchange to be the dominant process. The rapid variations of the cross-section with energy and angle indicate production of resonances. An interpretation of the data within the Bonn-Gatchina partial-wave analysis is briefly discussed. [ABSTRACT FROM AUTHOR]