Recent results from the COSY-11 experiment on near-threshold meson production in pp and pd collisions


The near-threshold production of K+K- pairs, as well as of eta mesons, has been measured in proton-proton collisions using the COSY-11 facility at the cooler synchrotron COSY. The obtained cross section for the pp->ppK+K- reaction at an excess energy of Q=17MeV represents the first measurement on the K+K- production below the Phi meson production threshold. The possible influence of a resonant production via intermediate scalar states f0(980) and a0(980) is discussed. The total cross sections for eta meson production in the pp->pp eta reaction were determined for eight different excess energies in the range from Q=0.5MeV to Q=5.4MeV. Inclusion of the eta-proton interaction is essential for the description of the energy dependence of the total cross section. The effect of eta-proton interaction is also seen in the Dalitz plot from a high statistics measurement at Q=15.4MeV. The ongoing studies at the COSY-11 facility of eta meson production in the p  p->pp eta, pd->3He eta, and dp->pd eta are also presented.

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