Near threshold hyperon-production at COSY-11 in the reactions pp -> pK(+) Lambda and pp -> pK(+)Sigma(0)

At the internal COSY-11 facility the reactions pp --> pK(+)Lambda and pp --> pK(+)Sigma(0) have been measured at excess energies up to 13 MeV. The total cross sections for the Lambda-production have been determined to be a factor of approximate to 28 higher than for the Sigma(0)-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 Sigma(0)p FSI might cause the low cross section for the Sigma(0)-production near threshold due to a Sigma N --> Lambda N conversion.