η′\eta^{\prime} Production in Proton-Proton Collisions near Threshold

Within the one-pion exchange model we calculate the near-threshold ${\eta}^{\prime}$ production from $pp$ collisions including the final state interaction between the protons. Since the description of the data is quite well we conclude that $\eta, \rho$ or $\omega$ exchange currents either play no role or cancel each other to a large extent in this reaction.Comment: 7 pages, LaTeX, including 3 ps-figures, UGI-98-20. To be pub. EPJ-

On the current status of OZI violation in πN{\pi}N and pp reactions

The available data on $\omega$ and $\phi$ production from $\pi N$ and $pp$ collisions are reanalyzed with respect to an OZI rule violation on the basis of transition matrix elements. The data are found to be compatible with a constant ratio $R$ up to excess energies $\epsilon{\approx}300$ MeV, however, the ratio $R$ deviates substantially from the SU(3) prediction based on the present knowledge of the $\phi-\omega$ mixing angle.Comment: 6 pages, svjour-style, including 10 ps-figure

Strangeness production from πN\pi N collisions in nuclear matter

Kaon production in pion-nucleon collisions in nuclear matter is studied in the resonance model. To evaluate the in-medium modification of the reaction amplitude as a function of the baryonic density we introduce relativistic, mean-field potentials for the initial, final and intermediate mesonic and baryonic states. These vector and scalar potentials were calculated using the quark-meson coupling (QMC) model. The in-medium kaon production cross sections in pion-nucleon interactions for reaction channels with $\Lambda$ and $\Sigma$ hyperons in the final state were calculated at the baryonic densities appropriate to relativistic heavy ion collisions. Contrary to earlier work which has not allowed for the change of the cross section in medium, we find that the data for kaon production are consistent with a repulsive $K^+$-nucleus potential.Comment: Revtex, 13 pages, 12 Postscript figures. A new secion for the resonance model has been added (with 2 new postscript figures). Version to appear in Phys. Rev.