Near threshold hyperon-production at COSY-11 in the reactions pp → pK⁺Λ and pp → pK⁺Σ⁰

At the internal COSY-11 facility the reactions pp → pK+Λ and pp → pK+Σ0 have been measured at excess energies up to 13 MeV. The total cross sections for the Λ-production have been determined to be a factor of ≈ 28 higher than for the Σ0-production at equivalent excess energies. This observation is in contrast to a cross section ratio of 2-3, obtained at higher excess energies between 300 MeV and 1500 MeV. It is discussed that a strong Σ0p FSI might cause the low cross section for the Σ0-production near threshold due to a ΣN → ΛN conversion.