The $\Sigma$ beam asymmetry in $\eta^{\prime}$ photoproduction off the proton was measured at the GrAAL polarized photon beam with incoming photon energies of 1.461 and 1.480 GeV. For both energies ...the asymmetry as a function of the meson emission angle shows a clear structure, more pronounced at the lowest one, with a change of sign around 90$^o$. The results are compared to the existing theories that fail to account for the data.
Neutral pion photoproduction has been measured from 550 to 1500 MeV with the GRAAL facility, located at the ESRF in Grenoble. Differential cross-section and beam asymmetry have been measured over a ...wide angular range. These high-precision data improve significantly the database for the beam asymmetry in the second and third resonance regions covering for the first time the energy domain 1100-1500 MeV. New partial-wave analyses including these data are presented for which the beam asymmetry brings crucial constraints.
The differential cross section for the reaction p(γ,ηp) has been measured from threshold to 1100 MeV photon laboratory energy. For the first time, the region of the S11(1535) resonance is fully ...covered in a photoproduction experiment and will allow a precise extraction of its parameters at the photon point. These high precision data together with the already measured beam asymmetry data will provide stringent constraints on the extraction of new couplings of baryon resonances to the η meson.
Generation of Compton backscattering γ-ray beams D'Angelo, A; Bartalini, O; Bellini, V ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2000, Letnik:
455, Številka:
1
Journal Article
Recenzirano
The backward scattering of laser light against high-energy electrons may be used to produce highly polarized photon beams of low background, with an energy resolution of a few percent. The general ...characteristics of Compton backscattering beams are outlined and the application of this technique to different electron accelerators is reviewed. The results from existing facilities are presented with an outlook to planned future installations.
The Σ beam asymmetry for positive pion photoproduction on the proton has been measured over an angular range of 40–170° at photon energies from 0.8 to 1.5 GeV. The resulting data set includes 237 ...accurate points, 136 of these belonging to an almost unexplored domain above 1.05 GeV. Data of such high precision provide severe constraints for partial wave analyses. The influence of this experiment on the GW multipole analysis is demonstrated. Significant changes are found in multipoles connected to the S31(1620) and P13(1720) resonances. Comparisons using the MAID analysis are also presented.
Σ beam asymmetries for
π
+ photoproduction on the proton have been measured in the energy range 550–1100 MeV over a wide angular range. The statistical and systematic errors of the data are much ...lower than in previous measurements, due to the high polarization of the photon beam and the cylindrical geometry of the 4
π detector. Our results confirm the predictions WI98 and SM95 of the VPI partial-wave analysis at the energies below 850 MeV and at 1050 MeV while, between these two regions, they differ at backward angles. It may indicate the smaller contribution of
S
11(1650) resonance, than it was quoted previously by the VPI and PDG groups. A newly developed unitary isobar model reproduces our data up to 950 MeV.
The double polarization (beam-recoil) observables Ox and Oz have been measured for the reaction γp → K+Λ from threshold production to E ∼ 1500MeV. The data were obtained with the linearly polarized ...beam of the GRAAL facility. Values for the target asymmetry T could also be extracted despite the use of an unpolarized target. Analyses of our results by two isobar models tend to confirm the necessity to include new or poorly known resonances in the 1900MeV mass region.
Beam asymmetry and differential cross section for the reaction gamma+p->eta+p were measured from production threshold to 1500 MeV photon laboratory energy. The two dominant neutral decay modes of the ...eta meson, eta->2g and eta->3pi0, were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different. The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found.
Beam asymmetries and hyperon recoil polarizations for the reactions $\gamma p \to K^{+}\Lambda$ and $\gamma p \to K^{+}\Sigma^{0}$ have been measured from the threshold production to 1500 MeV with ...the GRAAL facility located at the ESRF in Grenoble. These results complement the database for the beam asymmetry, covering for the first time the production threshold region. Recent theoretical analyses are presented for which the beam asymmetry data bring interesting new information and allow to better determine some resonance parameters. Most importantly, these results strengthen the need of a new D$_{13}$ state around 1900 MeV.
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