η-Photoproduction in a gauge-invariant chiral unitary framework

摘要

We analyze photoproduction of η mesons off the proton in a gauge-invariant chiral unitary framework. The interaction kernel for meson–baryon scattering is derived from the leading order chiral effective Lagrangian and iterated in a Bethe–Salpeter equation. The recent precise threshold data from the Crystal Ball at MAMI can be described rather well and the complex pole corresponding to the S 11 ( 1535 ) is extracted. An extension of the kernel is also discussed.