T. Van Cauteren

The role of hyperon resonances in p(γ, K+)Λ processes

Abstract:We discuss the role of hyperon resonances in the u-channel when modeling pγ, K+Λ processes in an effective Lagrangian approach. Without the introduction of hyperon resonances, one is forced to use soft hadronic form factors with a cutoff mass which is at best two times the kaon mass. After inclusion of the hyperon resonances in the u-channel, we obtain a fair description of the data with a cutoff mass of the order of 1.8 GeV.

Helicity amplitudes and electromagnetic decays of hyperon resonances

Abstract.We present results for the helicity amplitudes of the lowest-lying hyperon resonances Y*, computed within the framework of the Bonn Constituent-Quark model, which is based on the Bethe-Salpeter approach. The seven parameters entering the model were fitted to the best-known baryon masses. Accordingly, the results for the helicity amplitudes are genuine predictions. Some hyperon resonances are seen to couple more strongly to a virtual photon with finite Q2 than to a real photon. Other Y*s, such as the S01(1670) Λ-resonance or the S11(1620) Σ-resonance, couple very strongly to real photons. We present a qualitative argument for predicting the behaviour of the helicity asymmetries of baryon resonances at high Q2.-1

Electric and magnetic form factors of strange baryons

Abstract.Predictions for the electromagnetic form factors of the

Electroproduction of kaons from the proton in a Regge-plus-resonance approach

\Lambda

Support of generalized parton distributions in Bethe-Salpeter models of hadrons

,

Using highly excited baryons to catch the quark mass

\Sigma

Electromagnetic Transitions of Hyperons in a Relativistic Quark Model

and

Measurement of K{sup -}p radiative capture to gammaLAMBDA and gammaSIGMA{sup 0} for p{sub K}{sup -} between 514 and 750 MeV/c

\Xi

Measurement ofK−pradiative capture toγΛandγΣ0forpK−between 514 and 750 MeV/c

hyperons are presented. The numerical calculations are performed within the framework of the fully relativistic constituent-quark model developed by the Bonn group. The computed magnetic moments compare favorably with the experimentally known values. Most magnetic form factors GM (Q2) can be parameterized in terms of a dipole with cutoff masses ranging from 0.79 to 1.14 GeV.

Measurement of K-p radiative capture to γΛ and γΣ0 for pK- between 514 and 750 MeV/c

Abstract We present a Regge-plus-resonance (RPR) description of the p ( e , e ′ K + ) Y processes ( Y = Λ , Σ 0 ) in the resonance region. The background contributions to the RPR amplitude are constrained by the high-energy p ( γ , K + ) Y data. As a result, the number of free model parameters in the resonance region is considerably reduced compared to typical effective-Lagrangian approaches. We compare a selection of RPR model variants, originally constructed to describe KY photoproduction, with the world electroproduction database. The electromagnetic form factors of the intermediate N * s and Δ * s are computed in the Bonn constituent-quark model. With this input, we find a reasonable description of the p ( e , e ′ K + ) Y data without adding or readjusting any parameters. It is demonstrated that the electroproduction response functions are extremely useful for fine-tuning both the background and resonant contributions to the reaction dynamics.