Measurements of π0 photoproduction have been made at 235, 285, 335, and 435 MeV, using a beam of polarized x rays. Using a calculated value of polarization, an analysis is made which indicates a possible need for γ, ρ, π, or γ, ω, π coupling. The polarization calculations are checked by measurements made as a function of photon production angle at 335 MeV.
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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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We report measurements of the polarization parameters in π+p and π−p elastic scattering at an incident momentum of 100 GeV/c. The results cover the range 0.18<~−t<~1.4 GeV2 and are in agreement with current Regge-model predictions.
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The π − p→K 0 λ polarization has been measured at 5 GeV/ c in the range 0<− t <1.4 (GeV/ c ) 2 . The polarization is small for − t ⪅0.4 (GeV/ c ) 2 , becoming negative at the higher values of − t .
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The reaction γp → K 0 Σ + has been measured with the SAPHIR detector at the electron stretcher ring ELSA. The total cross section rises up to a peak value of 1.1 μ b at a photon energy of 1.4 GeV. The differential cross sections dσ/dΩ are consistent with being flat throughout the measured energy range. The first measurement of the Σ + polarization in photon induced reactions was obtained.
Total cross section for the reaction GAMMA P --> K0 SIGMA+. Errors include statistics and the uncertainty on the acceptance calculation and photon flux.
Differential cross section for the reaction GAMMA P --> K0 SIGMA+. Errors are dominated by statistical uncertainties.
Measure of SIGMA+ polarization in the reaction GAMMA P --> K0 SIGMA+.
The beam asymmetry, $\Sigma$, was measured at ELSA in the reaction $\vec \gamma p \to \eta p$ using linearly polarised tagged photon beams, produced by coherent bremsstrahlung off a diamond. The crystal was oriented to provide polarised photons in the energy range $E_\gamma = 800$ to 1400 MeV with the maximum polarisation of $P_\gamma = 49$ % obtained at 1305 MeV. Both dominant decay modes of the $\eta$ into two photons and $3\pi^0$ were used to extract the beam asymmetry from the azimuthal modulation of the cross section. The measurements cover the angular range $\Theta_\text{cm}\simeq 50$ -- 150 degrees. Large asymmetries up to 80 % are observed, in agreement with a previous measurement. The eta-MAID model and the Bonn--Gatchina partial wave analysis describe the measurements, but the required partial waves differ significantly.
Photon asymmetry for eta photoproduction at incident photon energy of 850 MeV.
Photon asymmetry for eta photoproduction at incident photon energy of 950 MeV.
Photon asymmetry for eta photoproduction at incident photon energy of 1050 MeV.
An experiment has been completed at the Daresbury synchrotron to measure the asymmetry in the photoproduction cross section of neutral pions on hydrogen, for photons polarised normal to and in the production plane. The source of polarised photons was coherent bremsstrahlung of electrons traversing the lattice structure of diamond and the polarisation P of the γ beam was calculated from the measured intensity of the coherent spike. The asymmetry parameter Σ, defined as Σ = ( σ ⊥ − σ |)/( σ ⊥ + σ |) where σ ⊥( σ |) are the cross sections for photons polarised perpendicular (parallel) to the production plane, has been measured over a range of photon energies from 1.2 to 2.8 GeV and over a range of − t (the square of the four-momentum transfer) from 0.13 (GeV/ c ) 2 to 1.4 (GeV/ c ) 2 . A marked energy variation in the value of Σ is found over the energy region 1.6–1.8 GeV.
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
K − p reactions have been studied at 13 different incident momenta between 1138 and 1434 MeV/ c . This interval corresponds to a mass of the K − p system varying from 1858 to 1993 MeV. About 300 000 photographs were taken in the 81 cm Saclay hydrogen bubble chamber exposed to a separated K − beam at the CERN proton-synchrotron. A total of about 44 000 events were analyzed, from which partial and differential cross sections were determined. Polarizations were obtained for the two-body reactions where the decay of the Λ or Σ hyperon allowed their measurement. Data for the two-body channels are presented here as well as for the main quasi-two-body reactions.
PARTIAL CROSS SECTIONS. DATA AT 1.305 TO 1.434 GEV/C FOR FINAL STATES K- P, K- P PI0 AND K- N PI+ COME FROM THE HAIFA GROUP, S. DADO ET AL.
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The angular distributions of the analyzing power for the pp → dπ + reaction have been measured at seven energies T p = 1.2, 1.4, 1.6, 1.7, 1.8, 2.0 and 2.3 GeV. The data show a strong energy dependence with a structure centered at √ s π d = 2.66 GeV. Possible interpretations are presented in the frame of the OPE model and involving the question of the excitation of a dibaryon resonance.
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Forward angular distributions of the analysing power for the pp→d π + reaction have been measured at six energies T p =1.2, 1.4, 1.6, 1.8, 2.0, 2.3 GeV. A strong energy dependence is observed for A y 0 ( t =0) and A y 0 ( θ CM π =90°). The data are compared with the backward angular distributions previously published and suggest the existence of a resonant state in the pp system at the approximate energy of 2.7 GeV.
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