Polarization of the Recoil Proton from the Neutral Photoproduction at 800 and 910 Mev

The measurements on the polarization of the recoil protons from the process $\gamma +p\to {\pi }^0+p$ have been extended to higher $\gamma$-ray energies, at 90° in the center-of-mass system. We have found at 910 Mev a polarization, $P=-0.45\mathrm{}\pm 0.07$; at 800 Mev, $P=-0.42\mathrm{}\pm 0.10$. The rather high values of $P$ agree with the hypothesis that the neutral photoproduction in the 500-1000 Mev range can be described by the well-known three resonant states, and strongly indicate that the second and third resonance have opposite parity. The probable quantum numbers are: $T=\frac{1}{2}$, $J=\frac{3}{2}$, $D$ pion wave for the second resonance; $T=\frac{1}{2}$, $J=\frac{5}{2}$, $F$ wave for the third resonance.