Abstract
Excited neutral hyperons Y0* produced in the pp → pK+Y0* reaction with a COSY beam momentum of 3.65 MeV/c have masses below 1540 MeV/c2. The ANKE spectrometer allows the simultaneous observation of different decay modes: Y0* → π0Σ0, 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 Y0* with a mass of M(Y0*) = (1480 ± 15) MeV / c 2 and a width of Γ(Y0*) = (60±15) MeV / c 2. The cross section for Y0* is of the order of few hundred nanobarns. It can be either a Σ0 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. Missing- and invariant–mass techniques have been used to identify the Λ(1405) resonance decaying via Σ0π0. The cross section for Λ(1405) production is equal to (4.5 ± 0.9 stat ± 1.8 syst ) 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.
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