T. Sefzick

Evidence for a narrow resonance at 1530MeV/c2 in the K0p-system of the reaction pp→Σ+K0p from the COSY-TOF experiment

The hadronic reaction pp -->Sigma+ K0 p was measured exclusively at a beam momentum of 2.95 GeV/c using the TOF detector at the COSY storage ring. A narrow peak was observed in the invariant mass spectrum of the K0 p subsystem at 1530 +- 5 MeV/c2 with a significance of 4 - 6 standard deviations, depending on background assumptions. The upper limit of 18 +- 4 MeV/c2 (FWHM) for its width is given by the experimental resolution. The corresponding total cross section is estimated to be about 0.4 +- 0.1(stat) +- 0.1(syst) microbarn. Since a resonance in this subsystem must have strangeness S = + 1 we claim it to be the Theta+ state for which very recently evidence was found in various experiments.

ETA ' PRODUCTION IN PROTON-PROTON SCATTERING CLOSE TO THRESHOLD

The

The WASA Detector Facility at CELSIUS

pp \to pp \eta^{\prime}

S-wave η′-proton FSI; phenomenological analysis of near-threshold production of π0, η, and η′ mesons in proton-proton collisions

(958) reaction has been measured at COSY using the internal beam and the COSY-11 facility. The total cross sections at the four different excess energies \mbox{

Near-threshold η meson production in proton-proton collisions

Q = ~1.5 ~MeV, ~1.7 ~MeV, ~2.9 ~MeV,

Comparison of Lambda and Sigma**0 threshold production in proton proton collisions

and

Energy dependence of the near-threshold total cross-section for the pp→ppη′ reaction

~4.1 MeV

Near threshold eta meson production in proton proton collisions

} have been evaluated to be \mbox{

Stacking of cold antiprotons

\sigma = 2.5 \pm 0.5~nb

Λ-hyperon production via the pp → pK+Λ reaction 2 MeV above threshold

,