Evidence for two Lambda(1405) resonance states

Abstract

The $K^- p \to \pi^0 \pi^0 \Sigma^0$ 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. We use these data in combination with those of the $\pi^- p \to K^0 \pi \Sigma$ reaction and elements of chiral unitary theory to prove that there are two $\Lambda(1405)$ states instead of one as so far assumed.