Measurement of γp→K + Λ and γp→K + Σ 0 at photon energies up to 1.47 GeV

The reactions pK ⁺ and pK ^{+ 0} have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the polarization and, for the first time, the ⁰ 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 and ⁰ is substantial at all energies and varies strongly with the production angle.This work is supported by the Bundesminister für Forschung und Technologie (BMFT), FK 06 BN 621 I     

Positive pion photoproduction from hydrogen at photon energies between 500 MeV and 1,400 MeV in forward direction

The differential cross section of the reactionγ+p→π ⁺ was measured at pion CM-angles of 20° and 30° for photon energies between 500 MeV and 1,400 MeV. The pions were detected in a magnetic spectrometer. By measuring each pion trajectory and by offline calculation of the initial pion parameters an energy resolution of about 2.5% FWHM was achieved. The results complete a set of data which were measured in recent years at the Bonn 2.5 GeV synchrotron. In comparison to photoproduction analyses two effects were revealed: The η cusp appears in the energy dependence of the cross section as a sharp drop atK _γ=710 MeV. In the region of the third resonance the data show a greater enhancement than predicted by most of the analyses.     

Target asymmetry measurement of deuteron photodisintegration at a photon energy of 550 MeV

The target asymmetry of the deuteron photodisintegration was measured at a photon energy of 550±50 MeV and at proton center-off-mass angles between 25 and 155 degrees.D-butanol andND ₃ were used as target material yielding a maximum deuteron polarization of 41%. Proton and neutron were detected in coincidence. The data show a structure which cannot be described by the existing analyses.     

Photodisintegration of polarized deuterons —measurement of angular distributions atE γ=450, 550 and 650 MeV

At the Bonn 2.5 GeV electron synchrotron an angular distribution of the target asymmetry of the reaction γ+d↑→p+n has been measured at photon-lab-energies of 450 and 650 MeV and at proton-CM-angles between 25° and 155°. At 550 MeV the data of our previous run [1] have been improved. Using deuterated ammonia as material for the polarized deuteron target a maximum vector polarization of 44% could be achieved. At 450 and 650 MeV the data are consistent with a smooth sin 2Θ-like distribution. The evidence for a structure around 90° at 550 Mev remains. This might be due to the influence of a higher momentum state (like a dibaryon). The feasibility of measuring the tensor asymmetry of the deuteron photodisintegration with a polarized target has been shown for the first time. Data were taken in a short run for one kinematical setting.     

Deuteron photodisintegration at photon energies between 200 and 700 MeV in backward direction

The differential cross section of the deuteron photodisintegration was measured at a protion c.m. angle of 180 degrees and for photon energies between 180 and 730 MeV. The protons were detected in a magnetic spectrometer. The proton energy resolution varied between 30 MeV and 50 MeV FWHM. Since these are the first data at 180 degrees in this energy range a comparison can only be done with data from other laboratories extrapolated to 180 degrees and with theoretical predictions. The agreement with existing calculations is poor. Contributions of dibaryons to the cross section seem not to improve the situation.