We have measured the differential cross section for the gamma n --> pi- p and gamma p --> pi+ n reactions at center of mass angle of 90 degree in the photon energy range from 1.1 to 5.5 GeV at Jefferson Lab (JLab). The data at photon energies greater than 3.3 GeV exhibit a global scaling behavior for both pi- and pi+ photoproduction, consistent with the constituent counting rule and the existing pi+ photoproduction data. Possible oscillations around the scaling value are suggested by these new data The data show enhancement in the scaled cross section at a center-of-mass energy near 2.2 GeV. The cross section ratio of exclusive pi- to pi+ photoproduction at high energy is consistent with the prediction based on one-hard-gluon-exchange diagrams.
Differential cross section at THETA(CM) = 90 degrees.
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Axis error includes +- 10./10. contribution (DUE TO BEAM POLARIZATION UNCERTAINTY).
D(SIG)/D(OMEGA)=(D(SIG(O))/D(OMEGA)+D(SIG(C))/D(OMEGA))/2, WHERE (O) AND (C) DENOTES GAMMA POLARIZATION ORTHOGONAL AND COPLANAR TO THE REACTION PLANE.
Axis error includes +- 10./10. contribution (DUE TO BEAM POLARIZATION UNCERTAINTY).
Measurements have been made of the polarisation parameters G and H for the process γ p→ π + n in the photon energy range 600–1875 MeV and pion c.m. angles between 30° and 100°. These data were obtained in a double polarisation experiment, in which the polarised photon beam from the Daresbury electron synchrotron was incident upon a polarised proton target. Theoretical predictions from a current analysis are compared with the data.
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Axis error includes +- 10/10 contribution (DUE TO BEAM POLARIZATION UNCERTAINTY).
Axis error includes +- 10/10 contribution (DUE TO BEAM POLARIZATION UNCERTAINTY).
Measurements have been made of the polarisation parameters Σ , T and P for the process γ p → π + n in the photon energy range 520–2250 MeV at c.m. angles between 30° and 120°. These data were obtained in a double polarisation experiment, using the polarised photon beam from the Daresbury electron synchrotron incident on a polarised proton target. The data are compared with predictions from current theoretical analyses.
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We have measured the cross sections at 90° c.m. for π± and π0 photoproduction with polarized photons. The photon energies ranged from 0.8 to 2.2 GeV. We compare the resonant "bumps" in the cross section with theoretical models. The measured asymmetry agrees with a quark-model calculation though the predicted cross sections are low.
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At the Bonn 2.5.GeV electron synchrotron the target asymmetry for the photoproduction of positive pions has been measured. Data were taken at photon energies between 0.7 and 2.2 GeV and a pion CM-angle of 65°.
Axis error includes +- 0.0/0.0 contribution (?////).
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The reaction γ+p→π++n has been measured for incident γ-ray energies from 0.7 to 8 GeV and recoil lab angles from 170° to 180° using the Cornell 10-GeV synchrotron. The data presented here cover the transition region between the resonance region and the high-energy region studied at SLAC. The results are compared with various phenomenological Regge-pole analyses and with similar data on π0 photoproduction taken at DESY.
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The π+ photoproduction cross section in hydrogen has been measured at 180° for photon energies from 0.22 to 3.1 GeV by detecting the pion in the backward direction. The statistical accuracy of the measurements varies typically from 3 to 10% depending on the energy. The data are compared with other recent experimental results and predictions of phenomenological theories.
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The cross section for photoproduction of single π+ from hydrogen has been measured at laboratory angles of 110°, 127.5° and 152°, between 0.9- and 3.2-GeV incident photon energy. Measurements have been made with approximately 15% statistical accuracy at about 40 photon energies at each angle. The results agree well with the previous Caltech data of Thiessen. The cross section shows a rapid drop with increasing energy with superimposed bumps or shoulders corresponding to the N(1688), Δ(1920), and Δ(2420). A shallow minimum is observed at the N(2190) resonance.
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