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

The $γp \to K^+ π^0 Λ$ and $γp \to K^+ πΣ$ reactions are studied in the kinematic region where the $π^0 Λ$(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 $K^- p \to π^0 Λ$ and $K^- p \to πΣ$ 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 $γp \to K^+ π^0 Λ$ and $γp \to K^+ πΣ$ 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.