Measurements of polarization in π+p elastic scattering have been made at 1.60, 1.80, 2.11, and 2.31 GeVc. The data cover the entire angular range, with emphasis on the backward region. Comparisons have been made with both u-channel and t-channel models, as well as with predictions of phase-shift analyses. While the agreement is generally poor in all cases, the best agreement is with some t-channel predictions.
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Measurements have been made of the π ∓ proton total cross sections over the laboratory kinetic energy range 70 to 290 MeV. The absolute accuracy of the data is generally 0.5 %, but decreases to 1 % for some points where applied corrections are large or where low particle fluxes limit the statistical accuracy.
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Results of a measurement of the π−p charge-exchange process at backward angles are presented. Differential cross sections were measured in the angular region −0.5<cosθ*<−1.0 at incident momenta of 2, 3, 4, 5, and 6 GeV/c. An additional background subtraction to a version of the data published previously has a significant effect at 6 GeV/c and brings the data into agreement with more recent measurements. The 6-GeV/c data were combined with existing measurements of the differential cross sections for backward π+p and π−p elastic scattering to yield values for the isotopic-spin-½ and −32 u-channel and s-channel amplitudes for backward pion-nucleon scattering and for the magnitude of the phases between them. It is found that the u-channel amplitudes can be explained by pure Regge-pole (Δδ, Nα) exchange only near the extreme backward direction, but that a Reggeized absorption model agrees at least qualitatively with the data. The phase difference between the I=12 and 32 s-channel amplitudes is approximately 90° over the region −0.8<u<0 (GeV/c)2.
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New formulae for constructing the pion photoproduction amplitude J from experimental data are presented. The phase of J is expressed in terms of its zeroes in the energy plane, the particle poles and a dispersion integral over the modulus of J , the latter being given, except for a finite unphysical interval, in terms of differential cross sections and recoil nucleon polarizations. For γ p→ π + n at t ≈−0.870 μ 2 , where the unphysical-region contribution vanishes, the zeroes are found approximately, so that the phase of J can be uniquely determined from the experimental data.
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Production of B(1235) and ρ(1710) mesons is observed in the four-pion decay modes π+π+π−π0 in 16−GeVc π±p collisions. Decay distributions and branching fractions into various modes are presented. Absence of the two-pion mode π−π0 for the ρ(1710) is noted.
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Electron-proton elastic scattering cross sections have been measured to determine the proton electromagnetic form factors at squared four-momentum transfers q 2 between 10 and 50 fm −2 . At these values of q 2 we measured angular distributions between 25° and 110° and in addition at 25° and 35° cross sections for q 2 from 2 to 20 fm −2 using the external electron beam of the Bonn 2.5 GeV electron synchrotron. Our results confirm deviations from the scaling law.
Axis error includes +- 2/2 contribution (NORMALIZATION ERROR).
Axis error includes +- 2/2 contribution (NORMALIZATION ERROR).
Axis error includes +- 2/2 contribution (NORMALIZATION ERROR).
Compton-scattering cross sections from hydrogen (γp→γp) and from deuterium have been measured at four-momentum transfer t in the range 0.014<~−t<~0.17 GeV2 and photon energies of 8 and 16 GeV. Fits to our proton data of the form dσdt=AeBt give B≈7.8 GeV−2 and an intercept A which is in agreement with the optical point. Both coherent scattering from deuterons and incoherent scattering from neutrons and protons are seen from deuterium. A small difference between the neutron and proton cross sections is seen, indicating the presence of about a 3% isovector t-channel exchange amplitude in addition to the predominant isoscalar amplitude. The vector-dominance model predicts lower cross sections (by at least 20%) for both the hydrogen and deuterium cases.
Axis error includes +- 3/3 contribution (SUBTRACTIONS WERE MADE FOR THE REACTIONS GAMMA P --> PI0 N, ETA N, OMEGA N AND PI0 DELTA(1232)).
Axis error includes +- 3/3 contribution (SUBTRACTIONS WERE MADE FOR THE REACTIONS GAMMA P --> PI0 N, ETA N, OMEGA N AND PI0 DELTA(1232)).
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