Evidence for the two-pole structure of the Λ(1405) resonance -: art. no. 052301

The K(-)p ->pi(0)pi(0)Sigma(0) reaction is studied within a chiral unitary model. The distribution of pi(0)Sigma(0) states forming the Lambda(1405) shows, in agreement with a recent experiment, a peak at 1420 MeV and a relatively narrow width of Gamma=38 MeV. The mechanism for the reaction is largely dominated by the emission of a pi(0) prior to the K(-)p interaction leading to the Lambda(1405). This ensures the coupling of the Lambda(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 Lambda(1405). This is unlike the pi(-)p -> K-0 pi Sigma 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 Lambda(1405).