Cross section asymmetries for the sum of single π + and π - production with polarized photons of 3.4 GeV have been measured. The results disagree with calculations based on the vector dominance model using experimental data of vector meson production in π beams.
No description provided.
The $\Sigma$ beam asymmetry in the photoproduction of negative pions from quasi-free neutrons in a deuterium target was measured at Graal in the energy interval 700 - 1500 MeV and a wide angular range, using polarized and tagged photons. The results are compared with recent partial wave analyses.
The measured beam polarization asymmetry for photon energy 753 MeV.
The measured beam polarization asymmetry for photon energy 820 MeV.
The measured beam polarization asymmetry for photon energy 884 MeV.
The polarized target asymmetry for γ n→ π − p was measured over the second resonance region from 0.55 to 0.9 GeV at pion c.m. angles between 60° and 120°. A double-arm spectrometer was used with a deuterated butanol target to detect both the pion and the proton, thus considerably improving the data quality. Including the new data in the amplitude analysis, the radiative decay widths of three resonances were determined more accurately than before. The results are compared with various quark models.
PHOTON ENERGY IS IN THE NEUTRON REST FRAME.
PHOTON ENERGY IS IN THE NEUTRON REST FRAME.
PHOTON ENERGY IS IN THE NEUTRON REST FRAME.
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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).
The recoil proton polarization for γ n → π − p was measured around the third resonance region. Both momentum vectors of the proton and the pion were determined by the magnetic spectrometers. The proton polarization was measured by means of proton-carbon scattering in the polarization analyzer located behind the proton spectrometer. Below 900 MeV incident photon energy, our data are consistent with the other existing experimental data ( θ π ∗ = 90° ) and the predictions of partial-wave analyses. Above 1000 MeV, however, a large discrepancy was observed between our data and the predictions of the partial-wave analyses. The discrepancy stands out as the pion c.m. angle increases. A new partial-wave analysis was made for γ n → π − p including our polarization data, and the accuracy of the experimentally determined electromagnetic coupling constant of the third resonances were greatly improved. In particular, a finite amount of the helicity 3 2 amplitude for the γ n → F 15 (1688) resonance was obtained against the predictions of the quark models, by Copley, Karl and Obryk and by Feynman, Kislinger and Ravendal but in agreement with the relativistic quark models of Sugimoto and Toya, and Kubota and Ohta.
No description provided.
The asymmetries in forward π−N, π−Δ, and K+−(Λ+Σ) photoproduction have been measured with a 16-GeV linearly polarized beam. The experimental method and the procedures for extracting cross sections and asymmetries from the data are discussed in detail. Information on the energy and momentum-transfer dependence of cross sections for natural- and unnatural-parity exchange, interference between exchanges of opposite G parity, and vector-meson dominance is obtained and discussed.
ASYMMETRIES AND DIFFERENTIAL CROSS SECTIONS FOR PION-NUCLEON PHOTOPRODUCTION WERE FIRST PUBLISHED IN D. J. SHERDEN ET AL., PRL 30, 1230 (1973) AND PRL 31, 667 (1973) (ERRATUM). THESE SLIGHTLY REVISED NUMBERS ARE INCLUDED IN THE RECORD OF THE 1973 PAPER.
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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.
No description provided.
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The asymmetry A=(dσ⊥−dσ∥)(dσ⊥+dσ∥) of the differential cross section for the reaction γd→π−pp has been studied with linearly polarized photons of 3.0 GeV at squared four-momentum-transfers between 0.15 and 2.0 (GeV/c)2. The asymmetry was found to be positive at −t values below 0.3 (GeV/c)2, dipping to negative values between 0.4 and 0.6 (GeV/c)2, and then rising again to positive values above 0.7 (GeV/c)2.
Axis error includes +- 11/11 contribution.
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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The angular dependence of the asymmetry for negative-pion photoproduction on neutrons by linearly polarized photons has been measured for photon energies 260, 300, 350, 400, 450, and 500 MeV at center-of-mass angles 60°, 75°, 90°, 150°, and 120°. The results are compared with theoretical models of low-energy single-pion photoproduction. The observed asymmetry below 400 MeV shows good agreement with predictions of dispersion-theoretical models by Berends, Donnachie, and Weaver and by Schwela. The asymmetry values in the 400-500 MeV energy region suggest that smaller M1− amplitude is more favorable.
No description provided.
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Measurements of the target asymmetry T = ( σ ↑ − σ ↓)/( σ ↑ + σ ↓) for the reactions γ p → π + n and γ n → π − p at a fixed photon energy of 850 MeV and pion c.m. angles between 70° and 150° are reported. The data are compared to the previously measured angular distribution at 700 MeV.
No description provided.
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A polarized neutron target was used at the Bonn 2.5 GeV Synchrotron to measure the target asymmetry for the reaction γ n↑→ π − p at a fixed photon energy of 700 MeV and pion c.m. angles between 50° and 140°. The pions were detected in a large aperture magnetic spectrometer. The data show a structure which is quite different from the distribution previously measured for the reaction γ p↑→ π + n.
No description provided.
The asymmetry of the reaction γ d π − p ( p S ) with linearly polarized photons has been measured at 3.4 GeV and momentum transfers √− t between 0.2 and 0.8 GeV/ c . As in π + production, the asymmetry is large and positive at small momentum transfers but drops rapidly with increasing √− t , crossing zero around √− t = 0.55 GeV/ c .
Axis error includes +- 0.0/0.0 contribution (?////).
No description provided.
Asymmetries in charged-pion photoproduction from hydrogen and deuterium have been measured with 16-GeV linearly polarized photons. Considerable energy dependence is seen in the natural-parity contribution to the π−π+ ratio from deuterium, and in the unnatural-parity part of the cross section for γn→π−p. The energy dependence of this latter cross section is consistent with the expected from a conventional pion Regge trajectory.
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We report on the measurement of asymmetries in the single-pion photoproduction reactions γp→nπ+, γp→pπ0, and γn→pπ−, induced by linearly polarized photons of energies from 610 to 940 MeV. The experiment was carried out using the back-scattered laser beam and the 82-in. dubble chamber at SLAC. We compare the new data with predictions from a partial-wave analysis.
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At the Bonn 2.5 GeV electron synchrotron the first measurements of the target asymmetry for the reaction γ + n ↑ → π − + p have been performed. The negative pions were detected in a magnetic spectrometer at a constant pion c.m. angle of 40° and photon energies between 0.45 GeV and 2.0 GeV. Deuterated butanol was used as target material. The polarization of the deuterons was about 16%. The results show a significant difference from the previously measured π + asymmetry.
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Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
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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The polarization of the proton from the γ+n→p+π− reaction in deuterium has been experimentally measured at 90° in the center-of-mass system for photon energies near 715 MeV by using a counter technique to observe the left to right asymmetry in the scattering of the protons from carbon. A value of -0.26±0.06 was observed, with the direction of the polarization defined by n^=(k^×q^)|k^×q^|, where k^ and q^ are, respectively, unit vectors in the directions of the photon momentum and the pion momentum. The result is interpreted as an indication that the interference between the P32 (325 MeV) and D32 (750 MeV) resonances may not be the dominant contribution to the polarization at this energy. Significant contributions from either an interference between the P32 (325 MeV) resonance and the possible new resonance suggested by the π, p scattering measurements, or an interference between the D32 (750 MeV) and F52 (1050 MeV) resonances, or a combination of these two possibilities seem to be required.
No description provided.
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The differential asymmetry ratio for the process γ+n→p+π− was measured at 90° in the center-of-mass system and for incident photon energies from 352 to 550 MeV. The observed asymmetries are larger than the values predicted from the theory by Berends, Donnachie, and Weaver. A smaller M1- amplitude gives better agreement between the experiment and the theory.
No description provided.
No description provided.
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