Search

The pp → ppϕ and quasi–free pn → dϕ reactions have been studied at the Cooler Synchrotron COSY–Jülich, using the internal beam and the ANKE facility. Total cross sections in the pp entrance channel have been determined at three excess energies ∊ in the range of 18.5–75.9 MeV. In case of the pn entrance channel the energy dependence of the cross section up to 80 MeV has been extracted by exploiting the intrinsic momentum of the neutron inside a deuterium target. Taken together with data for ω–production, a significant enhancement of the ϕ/ω ratio for both entrance channels of a factor 8 is found compared to predictions based on the Okubo–Zweig–Iizuka rule.

We plan to investigate sub-threshold K+ production in proton bombardment of atomic nuclei in order to study the reaction mechanism through a measurement of the double differential cross section and of K+ p and K+ d coincidences. The status of the theoretical studies is summarized, and the spectrometer to be installed in the COSY ring is briefly described.

The production of K+ or q mesons in proton-nucleus reactions is analysed with respect to primary nucleon-nucleon (NN + NhK+ or NNq) and secondary pion-nucleon (nN + K+A or qN) production channels on the basis of a phase-space model employing Hartree-Fock groundstate momentum distributions and free on-shell production processes. The phasespace model adopted here compares well for meson production with more involved simulations based on VUU transport equations. Whereas for K+ production in proton-nucleus reactions the secondary channel clearly dominates at subthreshold energies, q mesons arise from primary and secondary processes with roughly the same order of magnitude. Detailed VUU calculations show that the relative weight of the various channels for nucleus-nucleus reactions is quite different as compared to the protonnucleus case since A-resonance excitation and inelastic A-nucleon collisions are much more frequent.

A universal facility is in preparation for the study of particle production in proton-nucleus reactions below the nucleon-nucleon threshold. The device will be located at the internal target position TP2 at COSY-Julich and will consist of three dipole magnets. This 0° Facility will separate ejectiles from the circulating proton beam and allow momentum and angle analysis both for positively and negatively charged particles. A major goal of the experimental program is the investigation of the K+-meson production at projectile energies below the NN threshold. The detector concept for these studies is described and also an overview over further planned experiments is given.

The quasi-free pn->dphi reaction has been studied at the Cooler Synchrotron COSY-Juelich, using the internal proton beam incident on a deuterium cluster-jet target and detecting a fast deuteron in coincidence with the K+K- decay of the phi-meson. The energy dependence of the total and differential cross sections are extracted for excess energies up to 80 MeV by determining the Fermi momentum of the target neutron on an event-by-event basis. Though these cross sections are consistent with s-wave production, the kaon angular distributions show the presence of p waves at quite low energy. Production on the neutron is found to be stronger than on the proton but not by as much as for the eta-meson., Comment: 4 Pages, 3 Figures, version 2, resubmitted to Phys. Rev. Lett

The ratio of forward K+ production on copper, silver and gold targets to that on carbon has been measured at proton beam energies between 1.5 and 2.3 GeV as a function of the kaon momentum p_K using the ANKE spectrometer at COSY-Juelich. The strong suppression in the ratios observed for p_K, 9 pages, 3 figures; changed content

A kinematically complete study of the pd ? (pp)sn reaction with forward emission of an S-wave proton pair (pp)s has been performed at six beam energies 0.6, 0.7, 0.8, 0.95, 1.35 and 1.9 GeV. The experiment was carried out at the ANKE spectrometer installed at the internal beam of the proton synchrotron COSY (J?lich). The 3-momenta of both final state protons have been measured and events with a relative proton energy less than 3 MeV were selected as 1S0 diprotons. The differential cross sections of such pair production averaged over the c.m. polar angle of the total momentum of the pair in the range 0??8.1? have been obtained. A comparison of the result with a theoretical model based on the mechanism of pd-backward elastic scattering is described as well.