Beam Asymmetry Σ in Meson Photoproduction at GRAAL

Meson photoproduction on the nucleon is a major tool for the investigation of nucleon resonances. In particular eta photoproduction selectively probes certain resonances which are difficult to explore with pions. The low energy behaviour of the eta production is dominated by the S 11 (1535) resonance and the influence of other resonances (like D 13(1520)) is difficult to detect. Polarization observables enhance the sensitivity to the contributions of the less pronounced resonances since they depend mostly on the interference between the dominant E 0+ multipole and the smaller ones (like E 2- + M 2- for the D 13(1520))[l].