U. Kötz

PION PRODUCTION WITH POLARIZED PHOTONS AND TEST OF VECTOR DOMINANCE MODEL.

Abstract 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.

π+ production with linearly polarized photons

Abstract Single π+ production on protons by linearly polarized photons of 2.5 to 5 GeV was measured at squared four momentum transfers t between −0.01 and −0.6 (GeV/c)2. The results show that the differential cross section d σ ⊥ d t with the electric vector of the photon perpendicular to the reaction plane is much larger than d σ ‖ d t with the electric vector parallel to the reaction plane. The predictions of Regge models and of the vector meson dominance model are briefly discussed.

A Measurement of Large Angle

Abstract Elastic e + e − scattering has been measured at total energies covering the newly found resonance at 3100 MeV. The angular distribution is consistent with spin-parity 1 - , and the cross section integrated over energy yields Г 2 ee /Г tot = 0.23 ± 0.05 keV for the resonance.

e^+ e^-

Abstract The Λ polarization in the reaction γp → K + Λ has been measured using the decay Λ → pπ − as an analyzer. It is found to be large and negative in the momentum transer range 0.2 ⩽ | t | ⩽ 1.0 (GeV/ c ) 2 .

Scattering at the 3100-MeV Resonance

Abstract The π + —photoproduction cross section is found to have a peak in the forward direction in disagreement with simple Regge pole models.

Recoil polarization in K+ Λ photoproduction at 5 GeV

Abstract The three photon final state produced in e + e − collisions at 3.6 GeV and at the mass of the ψ′ resonance has been measured using the nonmagnetic part of the double arm spectrometer DASP. A total of 31 events is observed outside the resonance region compared to 35.1 events predicted from QED. At the mass of the ψ′ 49 events are observed compared to 37.2 events expected from QED. Limits on radiative decays via intermediate states are given.

Forward peak in π+—photoproduction

Abstract Inclusive photoproduction cross sections for pions, kaons and protons have been measured in the photon fragmentation region and are compared with recent electroproduction data at q 2 = 1.16 (GeV/ c ) 2 . If the cross sections are normalized to the total hadronic cross sections at q 2 = 0 and q 2 = 1.16 (GeV/ c ) 2 , respectively, we observe that more pions, about an equal number of protons, but fewer kaons are found in the photoproduction case for x ≥ 0.3.

The three photon final state produced in e+e− collision at 3.6 GeV and at the ψ′

Abstract We have measured collinear and nearly collinear photon pairs from e+e− annihilation at total energies covering the resonance at 3100 MeV. The observed cross section is in good agreement with the e+e− → γγ cross section expected from quantum electrodynamics. Upper limits for the decay modes (3100) → γγ, πOγ and other modes are derived.

Measurement of inclusive photoproduction at 3.2 GeV and comparison with electroproduction

Abstract We report results for μ pair production in e + e − collisions at the 3100 MeV resonance. We find a resonance cross section, integrated over total energy of 1240 ± 140 nb-MeV implying Γ μμΓ ee / Γ tot = 0.51 ± 0.09 KeV . The angular distribution is consistent with ∼(1 + cos 2 θ). No forward-backward asymmetry is observed.

A measurement of collinear and nearly collinear photon pairs produced by e+e− annihilation at the 3100 MeV resonance

Abstract Hadronic two body decays of the 3.1 GeV resonance were measured and the following branching ratios were obtained: Γπ+π−/Γμμ Γ p p / Γ μ μμ = 0.036 ± 0.010 assuming the p p decay distribution is ≈ + cos2θ.