Measurement of the beam asymmetry in η photoproduction off the proton
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The beam asymmetry, Σ , was measured at ELSA in the reaction \( \boldsymbol\gamma\) p → ηp using linearly polarised tagged photon beams, produced by coherent bremsstrahlung off a diamond. The crystal was oriented to provide polarised photons in the energy range E γ = 800 to 1400MeV with the maximum polarisation of P γ = 49 % obtained at 1305MeV. Both dominant decay modes of the η into two photons and 3π0 were used to extract the beam asymmetry from the azimuthal modulation of the cross-section. The measurements cover the angular range Θcm ≃ 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.
PACS.13.60.-r Photon and charged-lepton interactions with hadrons 13.60.Le Meson production 13.88.+e Polarization in interactions and scattering 14.20.Gk Baryon resonances with S = 0
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