Evidence for the Two-Pole Structure of the Λ(1405) Resonance

The K^-p→π⁰π⁰Σ⁰ reaction is studied within a chiral unitary model. The distribution of π⁰Σ⁰ 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. The mechanism for the reaction is largely dominated by the emission of a π⁰ prior to the K^-p interaction leading to the Λ(1405). This ensures the coupling of the Λ(1405) to the K^-p channel, thus maximizing the contribution of the second state found in chiral unitary theories, which is narrow and of higher energy than the nominal Λ(1405). This is unlike the π^-p→K⁰πΣ reaction, which gives more weight to the pole at lower energy and with a larger width. The data of these two experiments, together with the present theoretical analysis, provide firm evidence of the two-pole structure of the Λ(1405).