Theoretical analysis of Lambda(1405) photoproduction

Abstract

We develop a model that describes the gamma p -> K^+ pi Sigma reaction in the Lambda(1405) region. The model consists of gauge invariant photo-production mechanisms, and the chiral unitary model that gives the rescattering amplitudes where Lambda(1405) is contained. The model also contains phenomenological parameters, associated with short-range dynamics, to be used in fitting data. We successfully fit recent CLAS data for the pi-Sigma invariant mass distributions (line-shape) in the gamma p -> K^+ pi Sigma reaction for all the charge states. We find that the higher mass pole for Lambda(1405) of the chiral unitary model plays an important role in the reaction. We also find the non-resonant background contribution is not negligible, and its sizable effect shifts the Lambda(1405) peak position by several MeV. This work sets a starting point for a fuller analysis in which line-shape as well as K^+ angular distribution data are simultaneously analyzed for extracting Lambda(1405) pole(s).