Polarization of Recoil Protons from Neutral Pion Photoproduction

Abstract

The polarization of recoiling protons from the photoproduction of ${\ensuremath{\pi}}^{0}$ mesons on liquid hydrogen has been measured for primary photon energies between 500 and 1000 MeV over a range of ${\ensuremath{\pi}}^{0}$ c.m. angles from 55\ifmmode^\circ\else\textdegree\fi{} to 130\ifmmode^\circ\else\textdegree\fi{}. The results show structure not observed previously in experiments of less precision. In particular, the polarization at 90\ifmmode^\circ\else\textdegree\fi{} c.m. is close to zero at a primary photon energy of 900 MeV. Also, a strong dependence of polarization on ${\ensuremath{\pi}}^{0}$ c.m. angle between 600 and 900 MeV was observed. A subsidiary measurement of the polarization of the recoil protons from elastic $e\ensuremath{-}p$ scattering at 900 MeV and ${q}^{2}=10$ ${\mathrm{F}}^{\ensuremath{-}2}$ gave a value (1.3\ifmmode\pm\else\textpm\fi{}2.0)%.