W.Oelert für die COSY-11-Kollaboration, Institut für Kernphysik, Forschungszentrum Jülich D-52425 Jülich
COSY-11 is an internal facility with a hydrogen cluster target in front of a regular COSY dipole . The magnetic field separates the charged ejectiles under small angles from the circulating beam. A set of drift chambers combined with scintillators allows to measure the four-momentum vectors and thus determines the reaction exclusively. The absolute normalisation of the total cross section was obtained by comparing the simultaneously measured rate of elastically scattered protons to data recently published by the EDDA collaboration . First experimental results on the total cross sections for the reaction channels: pp->pK+Lambda (Sigma) and pp->ppK+K- will be presented and discussed in comparison to model calculations and reaction mechanism processes. Besides the interest in the elementary processes the resultes will serve as input for hyper-nuclei studies and questions of strangeness production mechanisms in heavy ion collisions. At the covered excess energy range (up to 10 MeV typically) mainly S-waves contribute to the production process and would thus fill the Dalitz plot uniformly. Final state interactions lead to measurable distortions. Emphasis will be given to the questions of precision concerning the absolut beam momentum and the determination of the final state interaction. The scattering length and effective range parameters are in agreement from the literature. Investigations aiming for a more precise determination of the p-Lambda scattering length are promising and will be discussed. A polarized proton target will be needed to distinguish between the p-Lambda system singlet and triplet S-wave states.
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