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K+Λ(1405) photoproduction has been studied at the BGOOD experiment via the all neutral decay, Λ(1405)→Σ0π0. The unique BGOOD experimental setup allows both the cross section and Λ(1405) invariant mass distribution (line shape) to be measured over a broad K+ polar angle range, extending to extreme forward K+ angles unattainable at previous experiments.Evidence is provided for the role of a triangle singularity driven by the N⁎(2030) resonance, which appears to contribute significantly to K+Λ(1405) photoproduction. This is observed in the integrated cross section which was determined with unprecedented energy resolution and supported by the angular distributions. The measured line shape is also in agreement with the previous results of CLAS and ANKE, and is consistent with two poles derived in χPT based models.

The γp→K+Σ0 differential cross section at extremely forward angles was measured at the BGOOD experiment. A three-quarter drop in strength over a narrow range in energy and a strong dependence on the polar angle of the K+ in the centre-of-mass of the reaction is observed at a centre-of-mass energy of 1900 MeV. Residing close to multiple open and hidden strangeness thresholds, the structure appears consistent with meson-baryon threshold effects which may contribute to the reaction mechanism.

K + Λ (1405) photoproduction has been studied at the BGOOD experiment via the all neutral decay, Λ (1405) → Σ 0 π 0. The unique BGOOD experimental setup allows both the cross section and Λ (1405) invariant mass distribution (line shape) to be measured over a broad K + polar angle range, extending to extreme forward K + angles unattainable at previous experiments. Evidence is provided for the role of a triangle singularity driven by the N ⁎ (2030) resonance, which appears to contribute significantly to K + Λ (1405) photoproduction. This is observed in the integrated cross section which was determined with unprecedented energy resolution and supported by the angular distributions. The measured line shape is also in agreement with the previous results of CLAS and ANKE, and is consistent with two poles derived in χ PT based models. [ABSTRACT FROM AUTHOR]

Abstract: The and reactions are studied in the kinematic region where the and pairs originate dominantly from the decay of the and 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 and 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 and 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. [Copyright &y& Elsevier]

Abstract: The and reactions are studied in the kinematic region where the and pairs originate dominantly from the decay of the and resonances. We consider laboratory photon energies around 2 GeV, significantly above the threshold for producing the and final states. We compute for both reactions the process in which the ingoing photon dissociates into a real and a virtual , the off-shell scattering subsequently off the proton target to produce the or πΣ pair. The and 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 in the πΣ channel and of the 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 and 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. [Copyright &y& Elsevier]

The γ p → K + Σ 0 differential cross section at extremely forward angles was measured at the BGOOD experiment. A three-quarter drop in strength over a narrow range in energy and a strong dependence on the polar angle of the K + in the centre-of-mass of the reaction is observed at a centre-of-mass energy of 1900 MeV. Residing close to multiple open and hidden strangeness thresholds, the structure appears consistent with meson-baryon threshold effects which may contribute to the reaction mechanism. [ABSTRACT FROM AUTHOR]