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The photoproduction of neutral pions from hydrogen has been studied by counting the recoil protons with a magnetic spectrometer and scintillation counters. The process has been studied between photon energies of 260 and 450 Mev and between center-of-momentum pion angles of 70° and 153°. The excitation functions show a resonance type shape with maxima at about 320 Mev. Angular distributions are analyzed in the form A+Bcosθ+Ccos2θ in the center-of-momentum system. The coefficient B, which gives the front-back asymmetry, is small at all energies; and the ratio −AC is 1.22±0.10 at all energies between 295 and 450 Mev. The maximum cross section at 90° in the c.m. system is 26×10−30 cm2/steradian for 320-Mev photons. The total cross section divided by the square of the c.m. photon wavelength has a maximum near 340 Mev, and drops by nearly a factor of two at 450 Mev. These results are consistent with magnetic dipole and electric quadrupole absorption leading to a resonant state of the pion-nucleon system of angular momentum 32 and isotopic spin 32.
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This paper reports measurements of the differential cross section for photoproduction of neutral pions in hydrogen at energies 300, 400, and 450 Mev, at center-of-momentum angles of 70° to 150°. One decay photon from the neutral pion is observed in coincidence with the recoil proton, whose energy and angle are measured to define the photon energy. The results obtained by this method are in good agreement with more accurate measurements obtained recently by the method of observing only the recoil proton.
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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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Absolute measurements of the elastic electron-proton cross section have been made with a precision of about 4% for values of the square of the four-momentum transfer, q2, in the range 6.0 to 30.0 F−2 and for electron scattering angles in the range 45° to 145°. To within the experimental errors, it is found that the charge and magnetic form factors of the proton have a common dependence on q2 when normalized to unity at q2=0, and that an accurate representation of the behavior of the form factor and that of the cross sections themselves can be given in terms of a three-pole approximation to the dispersion theory of nucleon form factors.
Axis error includes +- 2./2. contribution (RANDOM ERROR).
Axis error includes +- 2./2. contribution (RANDOM ERROR).
Axis error includes +- 2./2. contribution (RANDOM ERROR).
Measurements of π0 photoproduction have been made at 235, 285, 335, and 435 MeV, using a beam of polarized x rays. Using a calculated value of polarization, an analysis is made which indicates a possible need for γ, ρ, π, or γ, ω, π coupling. The polarization calculations are checked by measurements made as a function of photon production angle at 335 MeV.
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We report measurements of the differential cross section for photoproduction of π0 mesons from hydrogen, with the pion emerging near 0 deg, in the photon energy range 290 to 700 MeV. The results show no unusual behavior of the cross section in the forward direction. They are consistent with the angular distribution characteristic of a magnetic-dipole transition to a P32 state. The results agree reasonably well with theoretical predictions of Gourdin and Salin, but disagree with a prediction of DeTollis and Verganelakis. Least-squares fits in powers of cosθ have been made to the available angular distributions.
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