Spectator detection for the measurement of proton neutron interactions at ANKE

A telescope of three silicon detectors has been installed close to the internal target position of the ANKE spectrometer, which is situated inside the ultra-high vacuum of the COSY-Juelich light-ion storage ring. The detection and identification of slow protons and deuterons emerging from a deuterium cluster-jet target thus becomes feasible. A good measurement of the energy and angle of such a spectator proton (p_sp) allows one to identify a reaction as having taken place on the neutron in the target and then to determine the kinematical variables of the ion-neutron system on an event-by-event basis over a range of c.m. energies. The system has been successfully tested under laboratory conditions. By measuring the spectator proton in the p d to p_sp d pi^0 reaction in coincidence with a fast deuteron in the ANKE Forward Detector, values of the p n to d pi^0 total cross-section have been deduced. Further applications of the telescope include the determination of the luminosity and beam polarisation which are required for several experiments.Comment: 16 pages, 9 figure

General thoughts to the Kaon pair production in the threshold region

Simple--minded thoughts about the cross sections for the reactions pp-->ppK+K- and pp-->ppK0K0 are presented, which certainly do not account for the complex coupled channel problem but rather provide some ideas into the mutual reaction dynamics.Comment: Talk given at 9th International Workshop on Meson Production, Properties and Interaction, Cracow, Poland, 9-13 June 2006. 3 pages, 2 figure

Experimental study of the eta-meson interaction with two-nucleons

By means of the COSY-11 detection system, using a stochastically cooled proton beam of the cooler synchrotron COSY and a hydrogen cluster target, we have performed a high statistics measurement of the pp --> pp eta reaction at an excess energy of Q = 15.5 MeV. The experiment was based on the four-momentum determination of both outgoing protons. This permits to identify pp --> pp eta events and to derive the complete kinematical information of the eta-p-p-system allowing for subsequent investigations of the eta-p interaction. The observed spectrum of the invariant mass of the proton-proton system deviates strongly from the phase-space distribution revealing the influence of the final-state-interaction among the outgoing particles or nontrivial features of the primary production mechanism.Comment: 6 pages, 4 figures, Talk presented at Meson 2002, 7th International Workshop on Meson Production, Properties and Interaction, Cracow, Poland, 24-28 May 200

Hadronic interaction of eta and eta-prime mesons with nucleons

Due to their short life-time, flavour-neutral mesons cannot be utilized as free secondary beams or targets, and therefore a study of their interaction with nucleons is not possible via direct scattering experiments. This interaction is, however, accessible via its influence on the energy dependence - and on the phase space distributions of the cross sections for reactions in which these mesons are produced. In case of the p p --> p p eta reaction the experimentally determined distributions of the differential cross sections close to the production threshold cannot be described by taking into account the S-wave proton-proton and proton-eta interaction only. Here we show that the angular distributions determined at the COSY-11 facility reveal some evidence for P-wave admixture in the proton-proton subsystem already at an excess energy as low as Q = 15.5 MeV. We also present that one can estimate the relative strength of the eta-nucleon and eta-prime-nucleon interactions by comparison of the eta and eta-prime production yield.Comment: 4 pages, 3 figures, Talk given at 16th International Conference on Particles and Nuclei (PANIC 02), Osaka, Japan, 30 Sep - 4 Oct 200

Associated strangeness production in pp collisions near threshold

Motivated by the ongoing discussion concerning the nature of the scalar resonances f0(980) and a0(980), the COSY-11 collaboration has taken exclusive data on the pp->ppK+K- reaction near the production threshold. A first total cross section sigma=(1.80+-0.27+0.28-0.35)nb for the excess energy Q=17 MeV has been determined. In contrary to the eta, omega and eta' single meson production studies which clearly show the strong pp final state interaction (FSI), the cross section values obtained at COSY-11 and DISTO can be both described by a fit with a four-body phase space including the proton-proton final state interaction as well as with one-meson exchange calculations neglecting FSI effects. Therefore, one might think about a compensation of the strong pp interaction through a pK- FSI effect or an additional degree of freedom caused by the four-body final state. In the latter case, strong FSI effects can be expected at Q-values very close to the K+K- production threshold. Such a motivation triggered -- in combination with the investigation of the kaon-Antikaon interaction being relevant to the structure of the f0(980) -- further measurements at the excess energies Q=10 and Q=28 MeV at COSY-11.Comment: 5 pages, 4 figures, Presented at X. International Conference On Hadron Spectroscopy (Hadron 2003), Aschaffenburg, Germany, 31 Aug - 6 Sep 200

Analysing power A(y) in the reaction p(pol.)p --> pp eta near threshold

A first measurement of the analysing power in the reaction p(pol)p --> pp eta near the production threshold has been performed at the internal facility COSY-11 at the COoler SYnchrotron COSY.Comment: 4 pages, 2 figures, Presented at Meson 2002: 7th International Workshop on Production, Properties and Interaction of Mesons, Cracow, Poland, 24-28 May 200

First close-to-threshold measurement of the analyzing power Ay in the reaction p(pol)p -> pp eta

At the internal facility COSY-11 a first measurement of the reaction p(pol)p -> pp eta near the production threshold has been performed. Results for the analysing power will be presented and a comparison with one meson exchange models will be discussed.Comment: 3 pages, 3 figures, Presented at Conference on Quarks and Nuclear Physics (QNP 2002), Julich, Germany, 9-14 Jun 200

Production of eta and eta-prime mesons via the quasi-free proton-neutron interaction

A comparison of the close-to-threshold total cross sections for the eta-prime meson production in both the pp --> pp eta-prime and pn --> pn eta-prime reactions should provide insight into the flavour-singlet (perhaps also into gluonium) content of the eta-prime meson and the relevance of quark-gluon or hadronic degrees of freedom in the creation process. The excitation function for the reaction pp --> pp eta-prime has been already established. At present, experimental investigations of the quasi-free pn --> pn X reactions are carried out at the COSY-11 facility using a beam of stochastically cooled protons and the deuteron cluster target. A method of measurement and preliminary results from the test experiments of the pn --> pn eta reaction are presented in this report.Comment: 5 pages, 5 figures, Presented at X. International Conference On Hadron Spectroscopy (Hadron 2003), Aschaffenburg, Germany, 31 Aug - 6 Sep 200

Heavy Meson Production at COSY - 11

The COSY-11 collaboration has measured the total cross section for the pp --> pp eta-prime and pp --> pp eta reactions in the excess energy range from Q = 1.5 MeV to Q = 23.6 MeV and from Q = 0.5 MeV to Q = 5.4 MeV, respectively. Measurements have been performed with the total luminosity of 73 nb^(-1) for the pp --> pp eta reaction and 1360 nb^(-1) for the pp --> pp eta-prime one. Recent results are presented and discussed.Comment: Invited talk at 4th International Conference on Physics at Storage Rings (STORI 99), Bloomington, Indiana, USA, September 12-16, 199

Total and Differential Cross Sections for the pp-->pp eta-prime Reaction Near Threshold

The eta-prime meson production in the reaction pp-->pp eta-prime has been studied at excess energies of Q = 26.5, 32.5 and 46.6 MeV using the internal beam facility COSY-11 at the cooler synchrotron COSY. The total cross sections as well as one angular distribution for the highest Q-value are presented. The excitation function of the near threshold data can be described by a pure s-wave phase space distribution with the inclusion of the proton-proton final state interaction and Coulomb effects. The obtained angular distribution of the eta-prime mesons is also consistent with pure s-wave production.Comment: 6 pages, 5 figures, submitted to Eur. Phys. J.