Search

In an experiment at the external COSY beam associated strangeness production will be investigated [1] by measuring total and differential cross sections as well as the polarization of the produced hyperons by means of an almost 4π time-of-flight spectrometer. In a first step we will concentrate on the reaction pp → KΛp. The apparatus will consist of an inner arrangement as start detector and highly granulated scintillator hodoscopes as stop detector. Both parts give information on multiplicity and allow to identify the interesting reaction by means of the delayed charged decay of the Λ. Moreover the tracks of all prompt and delayed reaction products can be reconstructed with high precision. The detector allows the momentum measurement by time-of-flight. To get all this information the inner detector is composed of tiny granulated plastic scintillator detectors, silicon microstrip devices and a scintillating fibre hodoscope. The outer detector barrel with a diameter of about 3m and a length of about 7.5m will consist of three layers of plastic scintillator slabs, two of them bended in helix form. The status of the experiment will be presented. Moreover the results of test measurements for the different detector components will be discussed together with Monte Carlo calculations.

Search for narrow (p)over-bar-p resonances in the reaction (p)over-bar-p ->(p)over-bar-p pi(+)pi(-) (vol 76, pg 475, 1997)

We report on a determination of the analyzing power A y in the p → p → p p ω reaction studied with the TOF spectrometer located at the COSY-accelerator (Forschungszentrum Julich, Germany). This spectrometer is very well suited for polarization measurements due to its rotational symmetry and full coverage of the azimuthal angle. For a beam momentum of p = 3065 MeV / c corresponding to an excess energy of ϵ = 129 MeV A y is found to be compatible with zero.

Constraints on the spin-averaged $\Lambda p$ scattering length and effective range have been obtained from measurements of the $pp\to pK^+\Lambda$ reaction close to the production threshold by comparing model phase-space Dalitz plot occupations with experimental ones. The data fix well the position of the virtual bound state in the $\Lambda p$ system. Combining this with information from elastic $\Lambda p$ scattering measurements at slightly higher energies, together with the fact that the hyperdeuteron is not bound, leads to a new determination of the low energy $\Lambda p$ scattering parameters.

Preliminary results of recent measurements of the near threshold eta meson production in the dp-->dp eta reaction are presented. The experiment was performed at the COSY-Juelich accelerator with the use of the COSY-11 detection system. Data were taken for three values of deuteron beam momenta corresponding to excess energies of 3.2, 6.1 and 9.2 MeV. The energy dependence of the total cross section confirms a strong effect of the final state interaction., Talk given at 9th International Workshop on Meson Production, Properties and Interaction, Cracow, Poland, 9-13 June 2006. 5 pages, 3 figures

The proton–proton and proton–η′η′ invariant mass distributions have been determined for the pp→ppη′pp→ppη′ reaction at an excess energy of Q=16.4 MeVQ=16.4 MeV. The measurement was carried out using the COSY-11 detector setup and the proton beam of the cooler synchrotron COSY. The shapes of the determined invariant mass distributions are similar to those of the pp→ppηpp→ppη reaction and reveal an enhancement for large relative proton–proton momenta. This result, together with the fact that the proton–η interaction is much stronger that the proton–η′η′ interaction, excludes the hypothesis that the observed enhancement is caused by the interaction between the proton and the meson.

The COSY-11 experimental setup is an internal facility installed at the COoler SYnchrotron COSY in Juelich. It allows to investigate meson production in free and quasi-free nucleon-nucleon collisions, eg. pp --> pp meson and pd --> p_sp np meson reactions. Drift chambers and scintillators permit to measure outgoing protons, separated in magnetic field of COSY-11 dipole. Neutrons are registered in the neutron modular detector installed downstream the beam. Recently, the experimental setup has been extended with spectator detector, deuteron drift chamber and polarization monitoring system, and since then meson production can be investigated also as a function of spin and isospin of colliding nucleons., Presented at LEAP05: International conference on Low Energy Antiproton Physics, Bonn - Juelich, Germany, May 16-22, 2005

The 4π multidetector system for investigation of η-meson rare decays at the Uppsala CELSIUS storage ring is presented. A detailed description of the design, and achieved performance parameters is given.

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., 3 pages, 2 figures, Presented at Conference on Quarks and Nuclear Physics (QNP 2002), Julich, Germany, 9-14 Jun 2002

Results are presented for a measurement for the production of the antihydrogen atom H0 ≡ pe+, the simplest atomic bound state of antimatter. A method has been used by the PS210 collaboration at LEAR which assumes that the production of H0 is predominantly mediated by the e+e−-pair creation via the two-photon mechanism in the antiproton-nucleus interaction. Neutral H0 atoms are identified by a unique sequence of characteristics. In principle H0 is well suited for investigations of fundamental CPT violation studies under different forces, however, in our investigations we concentrate on the production of this antimatter object, since so far it has never been observed before. The production of 11 antihydrogen atoms is reported including possibly 2±1 background signals, the observed yield agrees with theoretical predictions.

The experimental setup and detection technique of the COSY-11 installation, an internal experimental facility at the cooler synchrotron and storage ring COSY Julich, are described. The detection system has been designed for meson production studies with full geometrical acceptance close to threshold. Preliminary results of first measurements are presented, emphasis is put on strangeness production in the reactions pp → ppK + K − and pp → pK + Λ .

The total cross section of the reaction pp->ppK+K- has been measured at excess energies Q=10 MeV and 28 MeV with the magnetic spectrometer COSY-11. The new data show a significant enhancement of the total cross section compared to pure phase space expectations or calculations within a one boson exchange model. In addition, we present invariant mass spectra of two particle subsystems. While the K+K- system is rather constant for different invariant masses, there is an enhancement in the pK- system towards lower masses which could at least be partially connected to the influence of the Lambda(1405) resonance., accepted for publication in Phys. Lett. B

Measurements of the η meson production with a polarised proton beam in the reaction p → p→ppη have been carried out at an excess energy of Q =40 MeV. The dependence of the analysing power A y on the polar angle θ ∗ q of the η meson in the center of mass system (CMS) has been studied. The data indicate the possibility of an influence of p- and d-waves to the close to threshold η production.

Information about the production mechanism of the eta meson in proton-proton collisions can be inferred by confronting the experimental studies on the analysing power for the p(pol)p --> pp eta reaction with the theoretical predictions of this observable. Results show that the predictions of pure pseudoscalar- or vector meson exchange model are insufficient to describe the analysing powers., 4 pages, 4 figures, Presented at MESON 2006: 9th International Workshop on Meson Production, Properties and Interactions, Cracow, Poland, 9-13 Jun 2006

We have measured excitation functions for the d+p->3He+X, (X=pi0, eta) channels near the eta production threshold. The data were taken during a slow ramping of the COSY internal deuteron beam scattered on a proton target. The excitation function for the reaction d+p->3He+pi0 does not show any structure which could originate from the decay of 3He-eta bound state. We measured also the threshold excitation curve for the d+p->3He+X process, however, contrary to the SATURNE results, we observe no cusp near the eta threshold., Talk given at 18th International IUPAP Conference on Few-Body Problems in Physics, 21-26 August, 2006, Santos, Brazil, 4 pages, 6 figures, will be published in Nuclear Physics A

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., Talk given at 9th International Workshop on Meson Production, Properties and Interaction, Cracow, Poland, 9-13 June 2006. 3 pages, 2 figures

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., 6 pages, 4 figures, Talk presented at Meson 2002, 7th International Workshop on Meson Production, Properties and Interaction, Cracow, Poland, 24-28 May 2002