Measurement of the analyzing power in the Primakoff process with a high-energy polarized proton beam

The analyzing power (spin-dependent azimuthal asymmetry) has been observed for the first time in the nuclear Coulomb coherent production process, the ‘‘Primakoff process,’’ with the use of the newly constructed 185-GeV/c Fermilab polarized proton beam. We have observed a large asymmetry of this process in the regions of ‖t’‖<0.001 (GeV/c${)}^2$ and 1.36<M(${\pi }^0$p)<1.52 GeV/$c^2$, where the Coulomb process is predominant. The measured asymmetry is consistent with the analyzing power of the existing low-energy γ+p→${\pi }^0$+p data.