6 research outputs found
Study of the reaction
The reaction has been studied with the CBELSA
detector at the tagged photon beam of the Bonn electron stretcher facility. The
reaction shows contributions from , and
as intermediate states. A partial wave analysis suggests that the
reaction proceeds via formation of six resonances,
, , ,
, , , and two
nucleon resonances and , for which pole
positions and decay branching ratios are given.Comment: 13 pages, 10 figures, 7 table
Evidence for a parity doublet Î(1920)Pââ and Î(1940)Dââ from ÎłpâpÏ0η
Evidence is reported for the existence of a parity doublet of Delta resonances with total angular momentum J=3/2 from photoproduction of the p pi(0)eta final state. The two parity partners Delta(1920)P-33 and Delta(1940)D-33 make significant contributions to the reaction. Cascades of resonances into Delta(1232)eta, N(1535)pi, and Na-0(980) are clearly observed
Photoproduction of η -mesons off protons
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 â 2Îł and in η â 3Ï0 â 6Îł . 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
Measurement of the beam asymmetry in η photoproduction off the proton
The beam asymmetry, Sigma, was measured at ELSA in the reaction gamma p -< eta p using linearly polarised tagged photon beams, produced by coherent bremsstrahlung o ff a diamond. The crystal was oriented to provide polarised photons in the energy range E-gamma = 800 to 1400MeV with the maximum polarisation of P-gamma = 49% obtained at 1305MeV. 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 circle minus cm similar or equal to 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