Constraints on the chiral unitary anti KN amplitude from πΣK⁺ photoproduction data

A chiral unitary approach for antikaon-nucleon scattering in on-shell factorization is studied. We find multiple sets of parameters for which the model describes all existing hadronic data similarly well. We confirm the two-pole structure of the Λ(1405). The narrow Λ(1405) pole appears at comparable positions in the complex energy plane, whereas the location of the broad pole suffers from a large uncertainty. In the second step, we use a simple model for photoproduction of K ⁺ πΣ off the proton and confront it with the experimental data from the CLAS Collaboration. It is found that only a few of the hadronic solutions allow for a consistent description of the CLAS data within the assumed reaction mechanism. (orig.)