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/{ital c} Fermilab polarized proton beam. We have observed a large asymmetry of this process in the regions of {vert bar}{ital t}{prime}{vert bar}{lt}0.001 (GeV/{ital c}){sup 2} and 1.36{lt}{ital M}({pi}{sup 0}p){lt}1.52 GeV/{ital c}{sup 2}, where the Coulomb process is predominant. The measured asymmetry is consistent with the analyzing power of the existing low-energy {gamma}+{ital p}{r arrow}{pi}{sup 0}+p data.