Precise measurement of Sigma beam asymmetry for positive pion photoproduction on the proton from 800 to 1500 MeV

The Sigma beam asymmetry for positive pion photoproduction on the proton has been measured over an angular range of 40-170degrees at photon energies from 0.8 to 1.5 GeV The resulting data set includes 237 accurate points, 136 of these belonging to an almost unexplored domain above 1.05 GeV. Data of such high precision provide severe constraints for partial wave analyses. The influence of this experiment on the GW multipole analysis is demonstrated. Significant changes are found in multipoles connected to the S-31(1620) and P-13 (1720) resonances. Comparisons using the MAID analysis are also presented. (C) 2002 Published by Elsevier Science B.V.