Measurements have been made of the target asymmetry parameter for photoproduction of π 0 mesons from protons, using a butanol polarised target with a 3 He cryostat. Results were obtained at 14 incident photon energies between 0.7 GeV and 1.45 GeV over an angular range ∼40° to 145° c.m. The recent analysis of Barbour and Crawford provides a very good fit to the data.
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The polarization of the proton from the γ+n→p+π− 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 n^=(k^×q^)|k^×q^|, where k^ and 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 P32 (325 MeV) and D32 (750 MeV) resonances may not be the dominant contribution to the polarization at this energy. Significant contributions from either an interference between the P32 (325 MeV) resonance and the possible new resonance suggested by the π, p scattering measurements, or an interference between the D32 (750 MeV) and F52 (1050 MeV) resonances, or a combination of these two possibilities seem to be required.
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Differential cross-sections have been measured for π0 photoproduction over the energy range 0.8 GeV to 1.4 GeV and at angles between 50° and 90° c.m.
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