P. Heide

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.

Recoil polarization in K+ Λ photoproduction at 5 GeV

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 .

Proton Comptons scattering between 2.2 and 7 GeV

Abstract Proton Compton scattering has been measured in a coincidence experiment at photon energies between 2.2 and 7 GeV and four-momentum transfers t between −0.06 and −0.85(GeV/ c ) 2 . For ∣ t ∣ ⩽ 0.4 (GeV/ c ) 2 fits of the form d σ /d t = ( A · exp( Bt )) yield forward cross sections A in good agreement with the values calculated from the total hadronic γ p cross section via the optical theorem and the forward dispersion relation. The slopes B do not show a significant energy dependence, the mean value being 5.7 ± 0.4 (GeV/ c ) −2 . The cross section is substantially larger than predicted by the vector-meson dominance model.

Small momentum transfer π+ production with linearly polarized photons

Abstract Previous measurements of the cross section asymmetry for single π + production on protons with linearly polarized photons of 3.4 GeV have been extended to momentum transfers within the forward peak, i.e. − = 0.0026, 0.006 and 0.01 (GeV/ c ) 2 . The results are in good agreement with pion exchange models.

MEASUREMENT OF PROTON COMPTON SCATTERING AT 6 GeV AND SMALL MOMENTUM TRANSFERS.

Abstract Compton scattering on protons has been measured at a mean photon energy of 6 GeV and four-momentum transfers − t between 0.06 and 0.60 (GeV/ c ) 2 . The differential cross section shows a diffraction-like behaviour. The cross section extrapolated to t =0 is in fair agreement with the optical point. Discrepancies with the vector meson dominance model are pointed out.

Forward peak in π+—photoproduction

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

Measurement of inclusive photoproduction at 3.2 GeV and comparison with electroproduction

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.

Compton scattering of 3.5 GeV polarized photons on protons

Abstract Elastic scattering of linearly polarized photons on protons has been measured between 3.2 and 3.7 GeV for four-momentum transfers ranging from −0.1 to −0.7 (GeV/ c ) 2 . The observed cross section asymmetry in this range is consistent with zero within ±0.05.