Associated strangeness production in the reactions γp → K + Λ and γp → K + Σ 0 was measured with the SAPHIR detector at the electron stretcher ring ELSA at Bonn. Data on total and differential cross sections and on hyperon polarizations are presented. The total cross section for Λ production shows a strong threshold enhancement whereas the Σ 0 data have a maximum at about E γ =1.45 GeV. Along with the angular decomposition of the differential cross section into polynomials, this suggests resonance production. However, the angular distributions of both hyperon polarizations vary only slightly with the photon energy. Λ and Σ 0 polarizations show opposite signs and change sign over the angular range.
Total cross section for the reaction GAMMA P --> K+ LAMBDA.
Total cross section for the reaction GAMMA P --> K+ SIGMA0.
Differential cross section for the reaction GAMMA P --> K+ LAMBDA in the GAMMA energy range 0.90 to 1.10 GeV in three energy bins.
The reactions γp→K+ Λ and γp→K+ Σ0 have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the Λ polarization and, for the first time, the Σ0 polarization have been determined in a photon induced reaction. All data are presented as functions of the photon energy (from threshold up to 1.47 GeV) and of the kaon production angle (0°–180°). The polarization of both Λ and Σ0 is substantial at all energies and varies strongly with the production angle.
Differential cross sections.
Total cross sections.
Differential cross sections.
The polarization parameter has been measured for K − p elastic scattering at nine incident beam momenta between 0.955 and 1.272 GeV/ c covering the c.m. angular range −0.9 < cos θ ∗ < + 0.9 . Experimental results and coefficients of Legendre polynomial fits to the data are presented and compared with other measurements and a partial-wave analysis.
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LEGENDRE POLYNOMIAL COEFFICIENTS FOR POLARIZATION DERIVED USING INTERPOLATED DIFFERENTIAL CROSS SECTION DATA OF B. CONFORTO ET AL., NP B105, 189 (1976).
The target asymmetry for the reaction γ p → K + Λ 0 was measured at the Bonn 2.5 GeV synchroton. Data were taken at a fixed kaon c.m. angle of 90° and at photon energies between 1.1 and 1.3 GeV. The kaons were detected in a large aperture magnetic spectrometer.
5 PCT TARGET POLARIZATION UNCERTAINTY INCLUDED IN QUOTED ERRORS.
Cross-section, angular distribution and polarization measurements are presented at six incident π + energies for the reaction π + p → K + Σ + . Results at already studied energies are compatible with existing data and roughly agree with predictions of partial-waves analyses. However, new results around 1.920 GeV are in disagreement with such predictions, casting some doubt on the determination of decay branching ratios of the T = 3 2 isobars around this mass into K + Σ + .
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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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The total and differential cross sections of the K¯0p→Λπ+ and K¯0p→∑0π+ reactions have been measured in the centre-of-mass energy range of l.5 to 2.3 GeV. Using our K¯0p→∑0π+ data as well as available cross-section data of isospin related channels, we have calculated the total I=0K¯N→∑π cross section as function of energy. The results are compared with predictions obtained from K¯N phase-shift analyses.
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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 target asymmetry T = ( σ ↑ − σ ↓)/( σ ↑ + σ ↓) for the reaction γ p → π + n has been measured at the Bonn 2.5 GeV electron synchrotron for a pion c.m. angle of 40° and γ energies between 0.5 and 2.2 GeV. Butanol was used as the target material. About 35% of the protons could be polarized using the dynamic-polarization method in a continuous-flow cryostat operating at 1°K and 25 kG. The π + mesons were detected in a magnetic-spectrometer system. Considerable structure in the asymmetry was observed.
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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