Measurements have been made on the ratio of pion-production cross sections at right angles to and along the photon electric-field vector. The positive and negative pions were first momentum-analyzed and counted by means of a counter telescope. Data have been taken at 45, 90, and 135° in the c.m. system, and at proton energies of 225, 330, and 450 MeV. A comparison of the data is made with the dispersion-relation calculation of McKinley.
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Measurements have been made of the ratio of the π+ photoproduction cross sections at right angles to and along the electric field vector. Data have been taken at 45°, 90°, and 135° at energies of 227, 240, 342, and 373 MeV. A comparison of the data with the predictions of a phenomenological analysis using only S and P waves shows less than 0.1% chance of obtaining such results without the inclusion of higher angular momenta, and hence, demonstrates even more convincingly the need for a meson current term which has been indicated by other measurements. A comparison is made with the relativistic dispersion relations of McKinley which include an approximation for the γ, ρ, π coupling. At the resonance energy our polarization asymmetry is insensitive to this coupling and is in good agreement with the McKinley prediction. At lower energy the agreement is not as good but our data seem to substantiate the need for a negative γ, ρ, π coupling constant.
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By selecting bremsstrahlung produced in a 0.003-in. aluminum radiator at a small angle from the original electron direction, a beam of polarized bremsstrahlung has been obtained from the Stanford linear accelerator. The variation of the polarization and intensity with angle has been studied and compared with theoretical predictions. The polarized beam has been used to study π+-meson production at 90° c.m. angle and photon energies of 242, 296, 337, and 376 Mev. The ratio of meson production along and at right angles to the electric field vector has been measured and compared with the values predicted by the relativistic dispersion relation.
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