The polarised beam asymmetry in photoproduction of eta mesons from protons at 2.5 GeV and 3.0 GeV

Measurements of the polarised beam asymmetry parameter Σ for eta photoproduction from protons, have been carried out at incident energies of 2.5 GeV and 3.0 GeV, and for various t-values between -0.2 (GeV/c)2 and -1.2 (GeV/c)2. The values of Σ are close to +1 for values of mod(t) less than 0.7 (GeV/c)2, showing that there can be little contribution from unnatural parity exchange in any Regge exchange model of the process, in disagreement with present theories. Differential cross sections for the process were also measured, and are consistent with those from other experiments. (Auth.)