K^- d → πΣn reactions and structure of the Λ(1405)

We report on the first results of a full three-body calculation of the NN-πYN amplitude for the K^-d → πΣn reaction, and examine how the Λ(1405) resonance manifests itself in the neutron energy distributions of K^-d → πΣn reactions. The amplitudes are computed using the NN-πYN coupled-channels Alt-Grassberger-Sandhas (AGS) equations. Two types of models are considered for the two-body meson-baryon interactions: an energy-independent interaction and an energy-dependent one, both derived from the leading order chiral SU(3) Lagrangian. These two models have different off-shell properties that cause correspondingly different behaviors in the three-body system. As a remarkable result of this investigation, it is found that the neutron energy spectrum, reflecting the A(1405) mass distribution and width, depends quite sensitively on the (energy-dependent or energy-independent) model used. Hence accurate measurements of the πΣ mass distribution have the potential to discriminate between possible mechanisms at work in the formation of the Λ(1405).