Kulturkammervorrichtung zur Erzeugung von flusslosen und zeitstabilen Gradienten

Kulturkammervorrichtung zur Erzeugung von flusslosen und zeitstabilen Gradienten (1), umfassend eine Beobachtungskammer (2), in der ein Konzentrationsgefüge dreidimensional einstellbar ist, mehrere Versorgungskanäle (4) zur Durchströmung mit einem Versorgungsfluid (10), jeweils eine Trennwand (13) zwischen den Versorgungskanälen (4) und der Beobachtungskammer (2), wobei die Trennwand (13) Poren (5) zur Diffusion von Versorgungsfluid zwischen dem jeweiligen Versorgungskanal (4) und der Beobachtungskammer (2) aufweist, wobei eine erste Anordnung von Versorgungskanälen (4O) oberhalb der Beobachtungskammer (2) und eine zweite Anordnung von Versorgungskanälen (4U) unterhalb der Beobachtungskammer (2) angeordnet sind

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

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

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

New results on the pd --> 3He eta production near threshold

Measurements on the eta meson production in proton-deuteron collisions have been performed using the COSY-11 facility at COSY Juelich. Here we present preliminary results on total and differential cross sections for the pd --> 3He eta reaction at five excess energies between Q = 5.1 and Q = 40.6 MeV. The obtained angular distributions for the emitted eta mesons in the center of mass system expose a transition from an almost isotropic emission to a highly anisotropic distribution. The extracted total cross sections support a strong eta-3He final state interaction and will be compared with model predictions.Comment: Presented at MESON 2004: 8th International Workshop on Meson Production, Properties and Interactions, Cracow, Poland, 4-8 Jun 2004, 3 pages, Submitted to Int. J. Mod. Phys.

Eta physics at threshold

The production of eta and eta-prime mesons in elementary nucleon-nucleon collisions has been investigated at the synchrotrons CELSIUS, COSY and SATURNE. The magnitude and energy dependence of the total cross section as well as the occupation distribution of the phase space serve as observables for investigating the mechanisms underlying the production processes and the interaction of mesons with nucleons. The precise data on the eta and eta-prime creation via the pp --> pp eta(eta-prime) reactions allowed to settle the general features of the eta and eta-prime meson production and revealed the sensitivity of the mentioned observables to the nucleon-nucleon-meson final state interaction. The particular production properties, like for example the determination of the dominating exchange processes which lead to the excitation of the S_11 nucleon isobar in the case of eta creation, must be established by confrontation with other observables. The present status of this investigation with an emphasis on the results of the COSY-11 collaboration is briefly presented. The available data are interpreted in view of the production mechanism and the meson-nucleon interaction.Comment: 3 pages, 3 figures, Presented at Conference on Quarks and Nuclear Physics (QNP 2002), Julich, Germany, 9-14 Jun 200

Associated strangeness production at threshold

The associated strangeness dissociation at threshold has been studied at the COSY-11 facility measuring the hyperon - and the K+K- meson pair production. Measurements of the near threshold Lambda and Sigma0 production via the pp -> pK+ Lambda / Sigma0 reaction at COSY-11 have shown that the Lambda / Sigma0 cross section ratio exceeds the value at high excess energies (Q >= 300 MeV) by an order of magnitude. For a better understanding additional data have been taken between 13 MeV and 60 MeV excess energy. The near threshold production of the charged kaon-antikaon pair is related to the discussion about the nature of the scalar states in the 1 GeV/c^2 mass range, i.e. the f0(980) and a0(980). The interpretation as a K anti-K molecule is strongly dependent on the K anti-K interaction which can be studied via the production channel. A first total cross section value on the reaction pp -> ppK+K- at an excess energy of 17 MeV i.e. below the phi production threshold was measured.Comment: 3 pages, 2 figures, Presented at Conference on Quarks and Nuclear Physics (QNP 2002), Julich, Germany, 9-14 Jun 200

Strangeness Production in Proton-Proton Collisions Close to Threshold

Exclusive data on the reactions pp -> ppK+K- and pp -> pK+ Lambda/Sigma0 have been taken at the cooler synchrotron COSY close to threshold. At equal excess energies, an enhancement of the Lambda/Sigma0 ratio by one order of magnitude has been observed compared to data at higher excess energies. New results obtained at the COSY-11 facility explore the transition region between this low-energy Sigma0 suppression and excess energies of 60 MeV. A first total cross section for elementary antikaon production below the phi threshold has been determined, two orders of magnitude smaller compared to kaon production at the same excess energy.Comment: 4 pages, 2 figures, Talk given by P. Moskal at 16th International Conference on Particles and Nuclei (PANIC 02), Osaka, Japan, 30 Sep - 4 Oct 200

On the close to threshold meson production in neutron-neutron collisions

A method of measuring the close to threshold meson production in neutron-neutron collisions is described where the momenta of the colliding neutrons can be determined with the accuracy obtainable for the proton-proton reaction. The technique is based on the double quasi-free nn --> nn X^0 reaction, where deuterons are used as a source of neutronsComment: 6 pages, 2 figures, to be published in Phys. Lett.