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 tot al cross sections for the Lambda-production have been determined to be a fa ctor of approximate to 28 higher than for the Sigma(0)-production at equiva lent excess energies. This observation is in contrast to a cross section ra tio 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 sec tion for the Sigma(0)-production near threshold due to a Sigma N --> Lambda N conversion.