Neutral pion photoproduction from the proton near threshold

Differential and total cross sections for the photoproduction of neutral pions from the proton have been measured for incident photon energies from 140-270 MeV, using the photon spectrometer TAPS at the tagged photon beam of the 855 MeV Mainz Microtron. The energy dependence of the s- and p-wave multipoles close to threshold was deduced from a multipole fit and a multipole analysis. The extracted s-wave amplitude Eo+ at threshold is found to be significantly smaller than the prediction of the classical low energy theorems, but is in reasonable agreement with the chiral perturbation theory