The associated photoproduction of positive kaons and π0Λ or πΣ pairs in the region of the Σ(1385) and Λ(1405) resonances

The γp→K+π0Λ and γp→K+πΣ reactions are studied in the kinematic region where the π0Λ(1116) and πΣ(1192) pairs originate dominantly from the decay of the Σ(1385) and Λ(1405) resonances. We consider laboratory photon energies around 2 GeV, significantly above the threshold for producing the K+Σ(1385) and K+Λ(1405) final states. We compute for both reactions the process in which the ingoing photon dissociates into a real K+ and a virtual K−, the off-shell K− scattering subsequently off the proton target to produce the π0Λ or πΣ pair. The K−p→π0Λ and K−p→πΣ amplitudes are calculated in the framework of a chiral coupled-channel effective field theory of meson-baryon scattering. The structure of the amplitudes reflects the dominance of the Λ(1405) in the πΣ channel and of the Σ(1385) in the πΛ channel. The full pion-hyperon final state interaction is included in these amplitudes. We extract from the calculated cross section the gauge-invariant double kaon pole term. We find this term to be large and leading to sizeable cross sections for both the γp→K+π0Λ and γp→K+πΣ reactions, in qualitative agreement with the scarce data presently available. Accurate measurements of these cross sections should make it possible to extract the contribution of the double kaon pole and hence to assess the possibility of studying kaon-nucleon dynamics just below threshold through these reactions.