Primakoff scattering for polarized photons or polarized protons

Abstract We present a way to measure the axial coupling of the proton for the neutral strangeness current in coherent π0 production induced by photon-proton scattering. By means of the γ−Z−π0 triangle anomaly, the parity violating asymmetries for polarized photon or polarized proton Primakoff effect filter the couplings so as to leave the proton axial coupling only. We calculate the relevant observables induced by the electroweak interference and give results for regions of energy and Q2 of possible experimental interest. The polarized proton asymmetry is predicted to be 10−6-10−5 when Q2 ∼ 0.1−0.5 GeV2.