Evidence for the two-pole structure of the Λ(1405) resonance

Abstract

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=38MeV. 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). © 2005 The American Physical Society.