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.

New data on ϕ -meson production in pp collisions have been obtained at the ANKE facility of COSY-Julich. These data will provide the energy dependence of the total cross section down to an excess energy of 19 MeV above threshold. In combination with the existing SPES-III and COSY-TOF results on ω -meson production the ϕ / ω production ratio at this low excess energy will be extracted. As an exciting new aspect an enhancement in the invariant ϕp mass spectrum is observed at a mass around 1.965 GeV / c 2 .

Results of a first experiment on (K+p) and (K+d) correlations from proton-carbon (pC) and proton-deuteron (pd) interactions at beam energies above and much below the threshold for elementary kaon production in nucleon-nucleon reactions ( TNN = 1580 MeV) are discussed. These data, obtained with the ANKE spectrometer at COSY-Julich, provide first direct evidence for K+ production via the two-step mechanism and an indication for a cluster mechanism. It is shown that both processes contribute significantly in pC collisions at 1200 MeV, while they are strongly suppressed at 2300 MeV and also in pd-interactions at 1344 MeV. It is emphasized that the underlying kinematics can be exploited to distinguish between these reaction mechanisms.

ANKE is a new experimental facility for the spectroscopy of products from proton-induced reactions on internal targets. It has recently been implemented in the accelerator ring of the cooler synchrotron COSY of the Forschungszentrum Julich (FZ-Julich), Germany. The device consists of three dipole magnets, various target installations and dedicated detection systems. It will enable a variety of hadron-physics experiments like meson production in elementary proton–nucleon processes and studies of medium modifications in proton–nucleus interactions.

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.

For the KFA Julich cooler synchrotron COSY a general data acquisition system was developed. Its architecture is based on available standards (VME, FASTBUS, CAMAC, VICbus) and UNIX workstations forming a distributed processor system. Based on this hardware a flexible and modular data acquisition software was designed allowing the configuration of various experiment arrangements. The software design for run control is arranged according to a client server connectivity model as well as to an object oriented structure. It is logically based on MAP/MMS (ISO9506), a powerful application layer protocol for distributed automation systems in industry. In our application servers are implemented on the mProcessor controller boards at the frontend. On the workstation side the experiment control client consists of dedicated processes with access to the configurable experiment data base. The user interface is realized by OSF/Motif. Established software standards for online data analysis high energy physics are employed. We discuss the most important design decisions mainly focusing on the software aspects. >

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.

A three-level data processing and acquisition system is being developed. Signals from various detector arrangements are digitized and preprocessed by CAMAC, FASTBUS, and VME modules. A multiprocessor system based on VMEbus is used for event building, data recording, and buffered data transfer to the host computer. All crates are connected by parallel VICbus. For this, an intelligent CAMAC rate controller with VICbus is under development. Microcomputer-based VME modules are equipped with CPUs of the 680X0 family, working under the OS-9 real-time operating system. The data acquisition system is mainly based on commercially available modules. >

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 pp ! ppreaction has been studied at the Cooler Synchrotron COSY-Julich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energiesnear the production threshold. The differential cross section closest to threshold at � � 18:5 MeV exhibits a clear S wave dominance as well as a noticeable effect due to the proton-proton final-state interaction. Taken together with data for pp! production, a significant enhancement of the �=! ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

The pp--ppphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S wave dominance as well as a noticeable effect due to the proton-proton final-state interaction. Taken together with data for ppomega production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

The reaction pp -> dpi+eta has been measured at a beam energy of T=2.65 GeV (p=3.46 GeV/c) using the ANKE spectrometer at COSY-Juelich. The missing mass distribution of the detected dpi+ pairs exhibits a peak around the eta mass on top of a strong background of multi-pion pp -> dpi+(n(pi)) events. The differential cross section d^4(sigma)/d(Omega_d)d(Omega_pi+)d(p_d)d(p_pi+) for the reaction pp -> dpi+eta has been determined model independently for two regions of phase space. Employing a dynamical model for the a0+ production allows one then to deduce a total cross section of sigma(pp -> da0+ -> dpi+eta)=(1.1 +/- 0.3_(stat) +/- 0.7_(syst)) microbarn for the production of pi+eta via the scalar a0+(980) resonance and sigma(pp -> dpi+eta) = (3.5 +/- 0.3_(stat) +/- 1.0_(syst)) microbarn for the non-resonant production. Using the same model as for the interpretation of recent results from ANKE for the reaction pp -> dK+(bar(K0)), the ratio of the total cross sections is sigma(pp -> d(K+(bar(K0)))_(L=0))/sigma(pp -> da0+ -> dpi+eta) = 0.029 +/- 0.008_(stat) +/- 0.009_(syst), which is in agreement with branching ratios in the literature., Comment: 5 pages, 8 figures, 1 table

The data acquisition system FATIMA (FERA amplitude and time multiparameter analyzer), which utilizes CAMAC, FERA (Fast Encoding and Readout ADC System), and a VAX-Station, has been designed and built for nuclear physics experiments like subthreshold pi /sup 0/-production in heavy ion collisions. The major features of the system are fast data readout of up to 352 ADCs and/or TDCs in conjunction with data reduction, event buffering, high-speed data transfer and simple interfacing to any workstation. For online acquisition, recording, and analysis of data as well as experiment control a modular program system was developed on VAX/VMS. Data analysis comprises online sort of real and pseudo channels and graphical representation of sorted data. >

The reaction $pp\ensuremath{\rightarrow}d{K}^{+}{\overline{K}}^{0}$ has been investigated at an excess energy of $Q=46\text{ }\mathrm{M}\mathrm{e}\mathrm{V}$ above the ${K}^{+}{\overline{K}}^{0}$ threshold with ANKE at the cooler synchrotron COSY-J\"ulich. From the detected coincident $d{K}^{+}$ pairs, about 1000 events with a missing ${\overline{K}}^{0}$ were identified, corresponding to a total cross section of $\ensuremath{\sigma}(pp\ensuremath{\rightarrow}d{K}^{+}{\overline{K}}^{0})=[38\ifmmode\pm\else\textpm\fi{}2(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\ifmmode\pm\else\textpm\fi{}14(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})]\text{ }\mathrm{n}\mathrm{b}$. Invariant-mass and angular distributions have been jointly analyzed and reveal $s$-wave dominance between the two kaons, accompanied by a $p$ wave between the deuteron and the kaon system. This is interpreted in terms of ${a}_{0}^{+}(980)$-resonance production.

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

K{sup +} -meson production in pA (A=C,Cu,Au) collisions has been studied using the ANKE spectrometer at an internal target position of the COSY-Juelich accelerator. The complete momentum spectrum of kaons emitted at forward angles, {theta}{

We propose to study pionic atoms in low‐lying states. The pions will be produced with the help of recoil free kinematics at small energies in the laboratory. A dedicated detector will be applied allowing the measurements of the width as well as the energy shift of these states.

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.

The Data Acquisition for experiments at the KFA Juelich COoler SYnchrotron COSY is based on VME, FASTBUS, CAMAC, VICbus, Ethernet and UNIX workstations. Controller and maser, equipped with CPUs, VME CPUs and workstations are formed to a distributed processor system, in software arranged by the object oriented Experiment Message Specification (EMS) protocol according to the server client connectivity. To perform the control of various experiment arrangements, composed of different number of crates with many embedded modules, a Control System, running on workstations was developed. Configurable setup of the frontend, run control, and distribution and decoding of event data are involved in the system. Experiment customizing is performed by ASCII files in an easy manner. The software is structured by dedicated clients with OSF/Motif user interface and access to the configurable experiment database. The design and state of the control system will be presented.