Double polarisation measurements in meson photoproduction

Photoproduction of positive and neutral pions was measured with a linearly polarised beam and a polarised target. Incident beam energies up to 2.5 GeV were used. In one series of measurements, with the beam polarised either in the reaction plane or perpendicular to it and the target protons polarised in the perpendicular direction, the asymmetry parameters Σ, T and P were measured. Measurements are in progress with the beam polarised at 450 to the reaction plane and the photons polarised in that plane, either along the beam or perpendicular to it. The two asymmetry parameters G and H will thus be determined. The above 5 parameters, together with the differential cross section, provide 6 of the 7 parameters needed to carry out an unambiguous, independent amplitude analysis at each energy