https://doi.org/10.1140/epja/i2007-10447-9
Regular Article - Experimental Physics
Measurement of the beam asymmetry in η photoproduction off the proton
1
Physikalisches Institut der Universität Bonn, Germany
2
Helmholtz-Institut für Strahlen- und Kernphysik der Universität Bonn, Germany
3
Petersburg Nuclear Physics Institute, Gatchina, Russia
4
Physikalisches Institut, Universität Erlangen, Germany
5
KVI, University of Groningen, The Netherlands
6
Department of Physics, Florida State University, Tallahassee, FL, USA
7
Physikalisches Institut, Ruhr-Universität Bochum, Germany
8
Physikalisches Institut, Universität Basel, Switzerland
9
II. Physikalisches Institut, Universität Giessen, Germany
* e-mail: schmieden@physik.uni-bonn.de
Received:
13
February
2007
Accepted:
20
July
2007
Published online:
22
August
2007
The beam asymmetry, Σ , was measured at ELSA in the reaction
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 –
© Società Italiana di Fisica and Springer-Verlag, 2007