Bochum 2009 – scientific programme

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HK: Fachverband Hadronen und Kerne

HK 69: Hadron Structure and Spectroscopy I

HK 69.4: Talk

Thursday, March 19, 2009, 17:45–18:00, H-ZO 20

Photon- and pion asymmetry in near-threshold ω photoproduction * — •Frank Klein — Physikalisches Institut, Universität Bonn, Germany

The photoproduction of ω mesons off protons has been studied from threshold to E_γ=1700 MeV in the reaction γ^→p → ω p. The photon-beam asymmetry, Σ, and, for the first time, the pion asymmetry Σ_π related to the ω → π⁰ γ decay have been measured [1].

The experiment was performed at the tagged photon beam of the ELSA electron accelerator of the University of Bonn. Using electron beams of E₀=3.2 GeV linearly polarized photons were produced by coherent bremsstrahlung. The ω meson was identified through it’s neutral decay mode into π⁰ γ. The corresponding three decay photons and the proton were detected in a combined setup of the Crystal Barrel and the TAPS calorimeters. Large photon asymmetries Σ in excess of 50 % were obtained. The pion asymmetries Σ_π were found close to zero. This provides a new indication that, on top of t-channel exchange processes, baryonic s-channel resonances play an important role in ω photoproduction. The photoproduction of ω mesons thus continues to be a promising channel to find so far undetected baryonic resonances predicted by current quark models. Ongoing measurements at ELSA of further double polarization observables will be indispensable to fully disentangle the process.

[1] arXiv:0807.0594 [hep-ex]
* supported by DFG (SFB/TR 16).