Polarization of the Proton from theγ+n→p+π−Reaction

The polarization of the proton from the $\gamma +n\to p+{\pi }^{-}$ reaction in deuterium has been experimentally measured at 90° in the center-of-mass system for photon energies near 715 MeV by using a counter technique to observe the left to right asymmetry in the scattering of the protons from carbon. A value of -0.26±0.06 was observed, with the direction of the polarization defined by $\hat{n}=\frac{(\hat{k}\times \hat{q})}{|\hat{k}\times \hat{q}|}$, where $\hat{k}$ and $\hat{q}$ are, respectively, unit vectors in the directions of the photon momentum and the pion momentum. The result is interpreted as an indication that the interference between the $P_{\frac{3}{2}}$ (325 MeV) and $D_{\frac{3}{2}}$ (750 MeV) resonances may not be the dominant contribution to the polarization at this energy. Significant contributions from either an interference between the $P_{\frac{3}{2}}$ (325 MeV) resonance and the possible new resonance suggested by the $\pi$, $p$ scattering measurements, or an interference between the $D_{\frac{3}{2}}$ (750 MeV) and $F_{\frac{5}{2}}$ (1050 MeV) resonances, or a combination of these two possibilities seem to be required.