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Differential cross sections for neutral-pion photoproduction on hydrogen in the region of the first resonance have been measured by two independent experiments detecting the recoil protons. The results of both measurements have been combined into one set of cross sections covering the photon energy range from 200 to 440 MeV at pion c.m. angles between 50 and 160 degrees.
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New measurements on the reactionsγp→K + Λ and γp→K + Σ o have been performed at the DESY synchrotron at c.m. angles around 90° and photon lab. energies from 1.19 to 1.68 GeV. The produced K + mesons were analyzed by a magnet spectrometer, two thresholdCˇerenkov counters and a time-of-flight measurement. The obtained differential cross-section data show a smooth energy behaviour for the K + Λ production whereas for theK + Σ o production the data trace out a bump at a c.m. energy W ≈ 1.9GeV.
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Measurements have been made of the polarization of the recoil proton in the process γ p → π o p for photon energies of 850 - 1250 MeV and centre-of-mass angles of 80° - 125°. The results, which are to a typical accuracy of ±0.09, show a marked disagreement with previous phenomenological analyses above 1000 MeV.
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The differential cross section has been measured for the reaction γ +p→p+ π o at the Bonn 2.5 GeV electron synchrotron in the energy range from 0.4 to 2.2 GeV for a c.m. angle of 150 degrees. The protons were detected in a magnetic spectrometer system. The excitation curve shows a distinct resonance structure. The total corrections to the counting rate are about 3%. The contribution of the process γ +p→p+2 π was separated. The uncertainty of this separation leads to an error of about 4% in the cross section.
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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.
At the Bonn 2.5 GeV synchrotron the differential photoproduction cross section d σ /d t of φ mesons has been measured at a photon energy of 2.0 GeV at fibe different t values between 0.23 < | t | < 0.73 (GeV/ c ) 2 . The φ meson was detected by magnetic momentum analysis of both charged decay K mesons and by a time of flight and angle measurement of the coincident recoil proton. We found an exponential behaviour for the t dependence of the cross section. The measured slope of the exponential decrease was b = (4.01 ± 0.23) (GeV/ c −2 . This result, combined with previous measurements at higher energies, implies that the slope of the pomeron trajectory is compatible with zero. In addition the experiment yielded a value of the φ mass, m φ = (1019.4 ± 0.8) MeV and a value of the φ width, Γ = (4.4 ± 0.4) MeV.
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We have measured total cross sections for neutrons on protons, deuteriom, beryllium, carbon, aluminium, iron, copper, cadmium, tungsten, lead, and uranium for momenta between 30 and 300 GeV/ c . The measurements were carried out in a small-angle neutral beam at Fermilab. Typical accuracy of the data is 0.5 to 1%. The cross sections are consistent with an A 0.77±0.01 dependence over the entire momentum range. The cross sections are compared with theoretical predictions. Agreement is found only if inelastic screening is included. Nuclear radii obtained from our data are in good agreement with previous determinations.
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The cross-sections for deuteron photo-disintegration have been measured at nine c.m. angles from 37 to 143 degrees. The minimum and maximum photon energies have been 139 and 832 MeV respectively. The results are in agreement with earlier data above 300 MeV, but are significantly larger below 200 MeV, the discrepancies being up to 50% at the lowest energies measured.
MEAN SCATTERING ANGLE FOR THIS DATA GROUP IS 36.9 DEG.
MEAN SCATTERING ANGLE FOR THIS DATA GROUP IS 53.1 DEG.
MEAN SCATTERING ANGLE FOR THIS DATA GROUP IS 66.4 DEG.
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