The differential cross sections for single-π+ photoproduction from hydrogen have been measured over a range of momentum transfers from -2×10−4 to -2 (GeV/c)2, and photon energies from 5 to 16 GeV. The differential cross section increases by roughly a factor of 2 as the magnitude of the square of the momentum transfer decreases from 0.02 (GeV/c)2. The cross section falls approximately as exp(−3|t|) at large momentum transfers, with a similar momentum-transfer dependence of the cross section at all photon energies studied.
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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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The azimuthal asymmetry Σ=(σ⊥−σII)(σ⊥+σII) in π+ photoproduction by linearly polarized bremsstrahlung was measured at photon energies from 475 to 750 MeV at 90° and 135° in the center-of-mass system. The experimental results show that even in this energy region, π+ are produced predominantly in the plane of the magnetic vector.
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The differential cross section for the photoproduction of a π− meson from the neutron bound in the deuteron was measured for pion laboratory angles of 76°, 96°, and 118° at incident gamma-ray energies in the region of 275 MeV. The π− meson and the high-energy proton were detected. The pion momentum and angle were measured by sets of spark chambers situated in front of and behind a magnetic field. The proton angle and range were also measured with spark chambers. To calculate "free" neutron cross sections from our data, we used a modified version of the extrapolation method suggested by Chew and Low. By observing the π+ only, the differential cross section for π+ photoproduction from hydrogen also was measured. As determined by this experiment, the differential cross section for photoproduction of a π− meson from a "free" neutron and the differential cross section for photoproduction of a π+ meson from hydrogen are as follows: Eγlab≃275 MeV These results disagree with the dispersion theory predictions of Chew, Goldberger, Low, and Nambu. They also disagree with McKinley's dispersion theory calculations which include a bipion or ρ-meson term in the production amplitudes.
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Photoproduction cross sections of charged pi mesons from hydrogen and deuterium have been measured as a function of meson angle at gamma-ray energies of 200, 235, and 265 Mev. The angular range extends from 30° to 180° in the laboratory system. Absolute cross sections have been determined. A least-squares fit of the measured cross sections has been made to the expression A+Bcosθ+Csin2θ, which assumes only S and P wave scattering. The coefficients so determined are qualitatively consistent with electric and magnetic dipole absorption together with the assumption of a resonant state of angular momentum 32 and of energy close to 300 Mev. Comparison with neutral meson production indicates some direct charged meson production in the P state.
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