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The π+—photoproduction cross section is found to have a peak in the forward direction in disagreement with simple Regge pole models.
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Single π + production on protons by linearly polarized photons of 2.5 to 5 GeV was measured at squared four momentum transfers t between −0.01 and −0.6 (GeV/ c ) 2 . The results show that the differential cross section d σ ⊥ d t with the electric vector of the photon perpendicular to the reaction plane is much larger than d σ ‖ d t with the electric vector parallel to the reaction plane. The predictions of Regge models and of the vector meson dominance model are briefly discussed.
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
The variation of the differential cross section for π+ photoproduction from hydrogen, with γ-ray energy, has been examined at a laboratory angle of 58° to the γ-ray beam. A thin hydrogen target, and a counter system designed to eliminate random events, have been employed. Mean values for the differential cross section dσdΩ at γ-ray energies of 162, 168, 175, and 192 Mev are 5.42±0.38, 5.77±0.41, 6.74±0.47, and 8.22±0.58 μb/sr, respectively, where the error limits refer to relative values. The results substantiate the rising trend of the interaction quantity {(dσdΩ)(μ2pε)(1+ωM)2} near threshold, in accord with dispersion theory; and the absolute cross sections are compatible with a threshold value for a0+ near 20 μb/ steradian, consistent with findings in related pion work.
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The asymmetry of π o and π + photoproduction from hydrogen has been measured. The π o -mesons were detected at 130° cms with E γ ranged from 0.9 to 1.65 GeV, and the π + -mesons at 40° cms with E γ ranged from 0.9 to 1.2 GeV. The results agree with model predictions of single pion photoproduction in the resonance region using fixed- t dispersion relations.
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
The differential cross-section for π+ photoproduction from hydrogen by γ-rays of laboratory energy 187 MeV has been measured at four angles. Two identical counter systems, designed to detect low energy pions unambiguosly in intense electron and γ-ray backgrounds, were used in conjunction with a cylindrical liquid hydrogen target, of very low boil-off rate. The cross-sections at laboratory angles of 39.2°, 66.7°, 111.6°, and 134° are 7.49±0.47, 8.10±0.57, 8.36±0.61 and 9.54±0.61, ·10−30cm2/sr, respectively, where the assigned errors refer only to the relative values. The absolute cross-sections are in substantial agreement with the dispersion theory and confirm the front to back asymmetry.
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The differential cross sections for the photoproduction reactions γ+p→π++n, γ+p→K++Λ0, and γ+p→K++Σ0 have ben measured for incident laboratory photon energies between 3.4 and 4.0 GeV and for meson center-of-mass angles from about 25° to 45°. The reactions were studied by observing only the charged mesons. The momenta, velocities, and angles of the mesons were measured with a magnetic spectrometer, and the equivalent of nearly monochromatic gamma rays was obtained by performing bremsstrahlung subtractions. The cross sections agree with the inequality predicted from unbroken SU(3). The measured behavior of dσdt as a function of t shows similarities to that observed in studies of mesonnucleon scattering.
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