Analysis of kaon spectra at SIS energies - what remains from the KN potential

We study the reaction Au+Au at 1.48 AGeV and analyze the influence of the KN optical potential on cm spectra and azimuthal distributions at mid-rapidity. We find a significant change of the yields but only slight changes in the shapes of the distributions when turning off the optical potential. However, the spectra show contributions from different reaction times, where early kaons contribute stronger to higher momenta and late kaons to lower momenta. Azimuthal distributions of the kaons at mid-rapidity show a strong centrality dependence. Their shape is influenced by the KN optical potential as well as by re-scattering.Comment: SQM 2003 proceedings, 4 figures, 6 page

Hyperon production in Ar+KCl collisions at 1.76A GeV

We present transverse momentum spectra, rapidity distribution and multiplicity of Lambda-hyperons measured with the HADES spectrometer in the reaction Ar(1.76A GeV)+KCl. The yield of Xi- is calculated from our previously reported Xi-/(Lambda+Sigma0) ratio and compared to other strange particle multiplicities. Employing a strangeness balance equation the multiplicities of the yet unmeasured charged Sigma hyperons can be estimated. Finally a statistical hadronization model is used to fit the yields of pi-, K+, K0s, K-, phi, Lambda and Xi-. The resulting chemical freeze-out temperature of T=(76+-2) MeV is compared to the measured slope parameters obtained from fits to the transverse mass distributions of the particles