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

Abstract

The near-threshold production of K+K− pairs, as well as of η 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=17 MeV represents the first measurement on the K+K− production below the Φ 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 η meson production in the pp→ppη reaction were determined for eight different excess energies in the range from Q=0.5 MeV to Q=5.4 MeV. Inclusion of the η-proton interaction is essential for the description of the energy dependence of the total cross section. The effect of η-proton interaction is also seen in the Dalitz plot from a high statistics measurement at Q=15.4 MeV. The ongoing studies at the COSY-11 facility of η meson production in the pp→ppη, pd→3Heη and dp→pdη are also presented.