Precise measurement of neutral-pion photoproduction on the proton near threshold

Abstract

An absolute measurement of ${\ensuremath{\pi}}^{0}$ photoproduction on the proton has been carried out in the threshold region (from 144.7 to 173 MeV) by use of tagged annihilation photons. The measured cross sections, differential in the recoiling-proton energy, are used to perform a multipole analysis which gives a value , in disagreement with low-energy-theorem predictions. Total cross sections and coefficients of the ${\ensuremath{\pi}}^{0}$ angular distribution are presented.