Evidence for two Lambda(1405) resonance states

Abstract

The $K^- p \to π^0 π^0 Σ^0$ reaction is studied within a chiral unitary model. The distribution of $π^0 Σ^0$ states forming the $Λ(1405)$ shows, in agreement with a recent experiment, a peak at 1420 MeV and a relatively narrow width of $Γ= 38$ MeV. We use these data in combination with those of the $π^- p \to K^0 πΣ$ reaction and elements of chiral unitary theory to prove that there are two $Λ(1405)$ states instead of one as so far assumed.