Study of the Σ(1385) and Λ(1405) resonances in K+ photoproduction processes

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, i.e. total center of mass energies above the known resonance region. We compute the t-channel kaon-exchange contribution to these reactions using K−p→π0Λ and K−p→πΣ amplitudes calculated in the framework of a chiral coupled-channel effective field theory of meson-baryon scattering. We extract from the calculated cross section the gauge-invariant double kaon pole term. We find this term to be large and likely to drive significantly the γp→K+π0Λ and γp→K+πΣ reactions in the kinematics under investigation. Accurate measurements of t-distributions for these processes, in progress or planned at ELSA and at SPring-8, are needed to confirm this expectation and assess the possibility of studying antikaon-nucleon dynamics just below threshold through these reactions.