Photoabsorption cross sections in hydrogen and deuterium have been measured from 3.7 to 17.9 GeV. The energy dependences are similar to those of strong-interaction total cross sections, as expected from the vector-meson-dominance model. The magnitude of σT(γp) can be compared with data from γp→ρ0p to determine a γ−p coupling constant, γρ24π=0.37±0.03. This value disagrees with that obtained on the ρ mass shell, and hence there is only qualitative agreement with the vector-meson-dominance model.
Axis error includes +- 1/1 contribution (CORRECTION OF ACCEPTANCE, POSSIBLE LOSSES, ETC).
The reaction γ⊥,∥p→π+n has been studied with linearly polarized photons of energy 3.0 GeV at −t values between 0.15 and 1.2 (GeVc)2. The asymmetry A+=(dσ⊥−dσ∥)(dσ⊥+dσ∥) is found to be positive throughout this four-momentum-transfer range, implying the dominance of natural parity exchange in the t channel. Comparison of dσ⊥(γ⊥p→π+n) and dσ⊥p→π−p) from a previous experiment indicates strong interference between the isoscalar and isovector photon amplitudes for photons polarized perpendicular to the production plane.
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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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The cross section for photoproduction of π0 mesons was measured at a photon energy of 3 GeV and squared four-momentum transfer (t) of -0.1 to -1.2 (GeV/c)2 using plane-polarized photons. The asymmetry was found to be consistent with +1.0 for t values above -0.4 and below -1.1. For −0.4<~t<~−1.0 there is a dip in the asymmetry and at t=−0.6 it drops to 0.55 ± 0.15. This result precludes a simple Regge model with ω0 and B; a theoretical description requires Regge cuts or an ω′ exchange.
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MIT PREP (1967).
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The polarization of recoiling protons from the photoproduction of π0 mesons on liquid hydrogen has been measured for primary photon energies between 500 and 1000 MeV over a range of π0 c.m. angles from 55° to 130°. The results show structure not observed previously in experiments of less precision. In particular, the polarization at 90° c.m. is close to zero at a primary photon energy of 900 MeV. Also, a strong dependence of polarization on π0 c.m. angle between 600 and 900 MeV was observed. A subsidiary measurement of the polarization of the recoil protons from elastic e−p scattering at 900 MeV and q2=10 F−2 gave a value (1.3±2.0)%.
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The polarization parameter in elastic π−p scattering has been measured, at the Berkeley 184-in. synchrocyclotron, with the use of a polarized proton target. At 318-, 337-, and 390-MeV incident pion kinetic energy, the angular range from 70° to 180° in the center-of-mass system was covered. At 229 MeV, polarization measurements were made in the angular range 150° to 180°. Phase-shift analyses, using these and other published data, were made at the two lowest energies.
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The polarization of the proton produced by the photodisintegration of the deuteron has been measured at several angles for photon energies between 170 and 450 MeV. The polarization is found to be around -0.20 (Basel convention) for 90° c.m. and photon energies between 200 and 300 MeV. This is in reasonable agreement with a calculation by D. George based upon the Austern model. However, the calculation fails to explain the strong increase in polarization with increasing photon energies. At a photon energy of 450 MeV and 90° c.m. the proton polarization is as large as -0.60.
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We have measured η0 photoproduction at 4 GeV. We find our results to be consistent with a theoretical preduction relating this cross section to ω0 production by π mesons using a vector-dominance model; there is no evidence for a dip or change of slope at −t=0.6 as seen in π0 photoproduction.
Axis error includes +- 0.0/0.0 contribution (?////).
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