3 research outputs found
The isospin structure of photoproduction of Ïη pairs from the nucleon in the threshold region
Photoproduction of Ïη -pairs from nucleons has been investigated from threshold up to incident photon energies of â 1.4 GeV. The quasi-free reactions ÎłpâpÏ0η , ÎłnânÏ0η , ÎłpânÏ+η , and ÎłnâpÏâη were for the first time measured from nucleons bound in the deuteron. The corresponding reactions from a free-proton target were also studied to investigate final-state interaction effects (for neutral pions the free-proton results could be compared to previous measurements; the ÎłpânÏ+η reaction was measured for the first time). For the Ï0η final state coherent production via the ÎłdâdÏ0η reaction was also investigated. The experiments were performed at the tagged photon beam of the Mainz MAMI accelerator using an almost 4 Ï coverage electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The total cross sections for the four different final states obey the relation Ï(pÏ0η)âÏ(nÏ0η)â2Ï(pÏâη)â2Ï(nÏ+η) as expected for a dominant contribution from a ÎââηÎ(1232)âÏηN reaction chain, which is also supported by the shapes of the invariant-mass distributions of nucleonâmeson and Ï â η pairs. The experimental results are compared to the predictions from an isobar reaction model
The polarization observables T , P , and H and their impact on ÎłpâpÏ0 multipoles
Data on the polarization observables T , P , and H for the reaction ÎłpâpÏ0 are reported. Compared to earlier data from other experiments, our data are more precise and extend the covered range in energy and angle substantially. The results were extracted from azimuthal asymmetries measured using a transversely polarized target and linearly polarized photons. The data were taken at the Bonn electron stretcher accelerator ELSA with the CBELSA/TAPS detector. Within the Bonn-Gatchina partial wave analysis, the new polarization data lead to a significant narrowing of the error band for the multipoles for neutral-pion photoproduction
<math altimg="si1.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msup><mrow><mi>K</mi></mrow><mrow><mo>+</mo></mrow></msup><mi>Î</mi></math> and <math altimg="si2.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msup><mrow><mi>K</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>ÎŁ</mi></mrow><mrow><mn>0</mn></mrow></msup></math> photoproduction with fine center-of-mass energy resolution
Measurements of <math altimg="si3.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mi>Îł</mi><mi>p</mi><mo stretchy="false">â</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>+</mo></mrow></msup><mi>Î</mi></math> and <math altimg="si4.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mi>Îł</mi><mi>p</mi><mo stretchy="false">â</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>ÎŁ</mi></mrow><mrow><mn>0</mn></mrow></msup></math> cross-sections have been obtained with the photon tagging facility and the Crystal Ball calorimeter at MAMI-C. The measurement uses a novel <math altimg="si5.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msup><mrow><mi>K</mi></mrow><mrow><mo>+</mo></mrow></msup></math> meson identification technique in which the weak decay products are characterized using the energy and timing characteristics of the energy deposit in the calorimeter, a method that has the potential to be applied at many other facilities. The fine center-of-mass energy ( W ) resolution and statistical accuracy of the new data results in a significant impact on partial wave analyses aiming to better establish the excitation spectrum of the nucleon. The new analyses disfavor a strong role for quarkâdiquark dynamics in the nucleon