The γp→pηη reaction in an effective Lagrangian model

Abstract

We report on a theoretical study of the ${K}^{\ensuremath{-}}p\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\Lambda}$ reaction near threshold by using an effective Lagrangian approach. The role of $s$-channel $\ensuremath{\Lambda}(1670)$, $t$-channel ${K}^{*}$, and $u$-channel proton pole diagrams are considered. We show that the total cross section data are well reproduced. However, only including the $s$-wave $\ensuremath{\Lambda}(1670)$ state and the background contribution from $t$ and $u$ channels is not enough to describe the bowl structures in the angular distribution of the ${K}^{\ensuremath{-}}p\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\Lambda}$ reaction, which indicates that there should be higher partial waves contributing to this reaction in some energy region. Indeed, if we considered the contributions from a ${D}_{03}$ resonance, we could describe the bowl structures; however, a rather small width ($\ensuremath{\sim}$2 MeV) of this resonance would be needed.