Photo- and Electroproduction of K⁺Λ

New isobar models for photo- and electroproduction of kaons on the proton were constructed utilizing new experimental data from LEPS, GRAAL, and particularly CLAS collaborations. Higher-spin nucleon (spin-3/2 and spin-5/2) and hyperon (spin-3/2) resonances were included using the consistent formalism and were found to play an important role in the description of data. The set of chosen nucleon resonances agrees well with the set of the most probable contributing states determined in the Bayesian analysis with the Regge-plus-resonace model. In our analysis, we paid special attention to model predictions of the cross section at small kaon angles since they are vital for accurate calculations of the hypernucleus-production cross section. What is more, in order to account for the unitarity corrections at the tree level, we have introduced energy-dependent decay widths of nucleon resonances. The energy-dependence of the decay width is then governed by the possibility of a given resonance to decay into various open channels and it also affects the choice of hadron form factors and the values of their cutoff parameters extracted in the fitting procedure.

On the road to electroproduction, we have implemented a new shape of electromagnetic form factors. For a reliable description of electroproduction at small virtual-photon mass Q², we found that it is necessary in our models to take into account a longitudinal coupling of virtual photons to nucleon resonances. The results of two versions of the isobar model will be compared with photo- and electroproduction data and the properties of the models will be discussed in great detail. In the case of electroproduction, we will present our new fit to data and discuss the significance of longitudinal couplings for good data description.