Excited Hyperons Produced in Proton-proton Collisions with Anke at Cosy

Excited neutral hyperons Y 0∗ produced in the pp → pKY 0∗ reaction with a COSY beam momentum of 3.65 MeV/c have masses below 1540 MeV/c. The ANKE spectrometer allows the simultaneous observation of different decay modes: Y 0∗ → πΣ, π∓Σ±, π0Λ,K−p by measuring kaons and pions of either charge in coincidence with protons. We have found indications for a neutral excited hyperon resonance Y 0∗ with a mass of M(Y 0∗) = (1480 ± 15) MeV/c and a width of Γ(Y 0∗) = (60 ± 15) MeV/c. The cross section for Y 0∗ is of the order of few hundred nanobarns. It can be either a Σ or a Λ hyperon and on the basis of existing data no conclusion could be made whether it is a three–quark baryon or an exotic state. Missingand invariant–mass techniques have been used to identify the Λ(1405) resonance decaying via Σπ. The cross section for Λ(1405) production is equal to (4.5±0.9stat±1.8syst)μb. The shape and position of the Λ(1405) distribution are similar to those found from other decay modes, so no support is given to the two-pole model.