The measurements on the polarization of the recoil protons from the process γ+p→π0+p have been extended to higher γ-ray energies, at 90° in the center-of-mass system. We have found at 910 Mev a polarization, P=−0.45±0.07; at 800 Mev, P=−0.42±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=12, J=32, D pion wave for the second resonance; T=12, J=52, F wave for the third resonance.
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A graphite-plate spark chamber has been used to analyze the polarization of protons recoiling from π−−p scattering. The observations were made at 90° (c.m. system) pion scattering angle for seven incident pion energies between 500 and 940 Mev, at 120° or 135° for five energies in this interval, and also at 75° for 500 Mev only. The results are compared with predictions of several models used to explain the maxima in the π−−p scattering cross section. Qualitative arguments show that the energy intervals between these maxima are not completely dominated by neighboring single-state resonances. Phase shifts found to be large in scattering also seem to be large in polarization.
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The polarization of the recoil proton in neutral single-pion photoproduction from hydrogen, γ+p→p+π0, has been measured for pion center-of-mass angles near 90° at 7 photon energies from 450 to 900 MeV. The polarization rises to a maximum of 0.58 near 600 MeV and is still 0.42 at 900 MeV. The sign of the polarization is negative in the sense of k×q, where k is the photon momentum and q is the pion momentum. The measured values are given as functions of laboratory photon energy and c.m. pion angle as follows: 450 MeV, 109°, -0.16±0.14; 525 MeV, 84°, -0.36±0.19; 585 MeV, 86°, -0.58±0.15; 660 MeV, 77°, -0.51±0.17; 755 MeV, 76°, -0.55±0.15; 810 MeV, 89°, -0.45±0.17; 895 MeV, 90°, -0.42±0.16. The recoil protons were momentum-analyzed with a magnetic spectrometer. Nuclear emulsion was used as scatterer and detector. The emulsion technique is discussed in detail. The number of individual scatterings in emulsion used for each measurement varied between 750 and 1000.
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The polarization of recoiling protons from the photoproduction of π0 mesons on liquid hydrogen has been measured for primary photon energies between 500 and 1000 MeV over a range of π0 c.m. angles from 55° to 130°. The results show structure not observed previously in experiments of less precision. In particular, the polarization at 90° c.m. is close to zero at a primary photon energy of 900 MeV. Also, a strong dependence of polarization on π0 c.m. angle between 600 and 900 MeV was observed. A subsidiary measurement of the polarization of the recoil protons from elastic e−p scattering at 900 MeV and q2=10 F−2 gave a value (1.3±2.0)%.
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We measured the polarization of the recoil proton in the process γp→pη0, at 90° in the center-of-mass system, at incoming photon energies from 0.8 to 1.1 GeV. Detection of all three particles in the final state pγγ permitted observation of this process with little background. Subsequent rescattering off carbon nuclei yielded sizable polarization values for the protons, indicating considerable S−P—wave interference in the production process.
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Polarization and differential cross-section data for elastic scattering of positive pions on protons between 0.82 and 2.74 GeV/ c are presented. A dip in the polarization, at constant u ≈ −0.65 GeV 2 , is observed. The data are compared with published phase-shift analyses.
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