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We describe a novel technique for comparing total cross sections for the reactions pp --> pp pi(0), pp --> pp eta, and pp --> pp eta' close to threshold. The initial and final state proton-proton interactions are factored out of the total cross section, and the dependence of this reduced cross section on the volume of phase space is discussed. Different models of the proton-proton interaction are compared. We argue that the scattering length of the S-wave eta'-proton interaction is of the order of 0.1 fm., 10 pages, 5 figures

The production of eta mesons has been measured in the proton-proton interaction close to the reaction threshold using the COSY-11 internal facility at the cooler synchrotron COSY. Total cross sections were determined for eight different excess energies in the range from 0.5 MeV to 5.4 MeV. The energy dependence of the total cross section is well described by the available phase-space volume weighted by FSI factors for the proton-proton and proton-eta pairs., Comment: 9 pages, 1 table, 5 figures

Total cross sections for the pp --> pp eta' reaction have been measured in the excess energy range from Q = 1.53 MeV to Q = 23.64 MeV. The experiment has been performed at the internal installation COSY-11 using a stochastically cooled proton beam of the COoler SYnchrotron COSY and a hydrogen cluster target. The determined energy dependence of the total cross section weakens the hypothesis of the S-wave repulsive interaction between the eta' meson and the proton. New data agree well with predictions based on the phase-space distribution modified by the proton-proton final-state-interaction (FSI) only., Comment: 12 pages, 1 table, 4 figures

Threshold measurements of the associated strangeness production reactions pp --> pK(+)Lambda and pp --> pK(+)Sigma(0) are presented. The most remarkable feature of the data is that at the same excess energy the total cross section for the Sigma(0) production appears to be about a factor of 28(-9)(+6) smaller than for the Lambda particle. It is concluded that strong Sigma(0)p final state interactions, and in particular the Sigma N --> Lambda p conversion reaction, are the likely cause of the depletion in the Sigma signal. This hypothesis is in line with other experimental evidence in the literature.

The $pp \to pp \eta^{\prime}$ (958) reaction has been measured at COSY using the internal beam and the COSY-11 facility. The total cross sections at the four different excess energies \mbox{$ Q = ~1.5 ~MeV, ~1.7 ~MeV, ~2.9 ~MeV,$ and $ ~4.1 MeV$} have been evaluated to be \mbox{$ \sigma = 2.5 \pm 0.5~nb$, $~~~ 2.9 \pm 1.1~nb$, $~~~ 12.7 \pm 3.2~nb$, ~ and $~~~ 25.2 \pm 3.6 ~nb $}, respectively. In this region of excess energy the $\eta^{\prime}$ (958) cross sections are much lower compared to those of the $\pi ^0$ and $\eta$ production.

The energy dependence of the total cross section for the pp \to pK^+\Lambda reaction was measured in the threshold region covering the excess energy range up to 7MeV. Existing model calculations describe the slope of the measured cross sections well, but are too low by a factor of two to three in rate. The data were used for a precise determination of the beam momentum of the COSY-synchrotron.

The pp → pK+Λ reaction was measured at COSY with a proton beam momentum of 2.345 GeV/c, i.e. with an excess energy of 2 MeV above threshold. The total cross section was determined to be 8.2 ± 1.8 nb. The present data point close to the production threshold indicates, that existing phenomenological parametrizations of the total kaon production cross section are insufficient.

The COSY-11 installation is an internal experiment at the cooler synchrotron and storage ring COSY Julich. It has been designed for full geometrical acceptance close to threshold for meson production studies, especially in the 1 GeV/c2 mass range. The experimental setup makes use of a regular C-type COSY dipole magnet, following a cluster target, to separate reaction products from the beam and to analyze their momenta, thus allowing the observation of charged reaction products at small angles with beam energies close to threshold. Resonances will be identified by missing mass reconstructions from measured four-momenta of two outgoing protons in the predominantly studied pp → ppX reaction. In addition, charged mesons either produced directly or from decays of X will be detected. The different components of the experimental facility are presented.

The differential cross sections for the n+d elastic scattering and for the 2H(n,np)n break-up reaction in the np quasi-free scattering configuration was measured at 67 MeV. The experimental data are compared with results of the calculations based on a rigorous solution of the three-nucleon Faddeev equations using meson-exchange potentials. Good agreement is found between experiment and theory for the n+d elastic-scattering cross section while in the case of np quasi-free scattering the theoretical predictions overestimate the data at neutron angles larger than 40° by about 30%.

The angular distribution of the analyzing power A y for the 2 H( n , np)n breakup reaction at 67 MeV was measured in two kinematical regions: np quasi-free scattering and np final-state interaction. The results are compared with rigorous three-nucleon calculations using the Paris potential and allowing for charge dependence in the 1 S 0 state. According to the actual experimental conditions energy averaging was simulated in the theoretical calculations. In both configurations agreement between experimental and calculated values is found.

The near threshold total cross section and angular distributions of K+K- pair production via the reaction pp --> ppK+K- have been studied at an excess energy of Q = 17 MeV using the COSY-11 facility at the cooler synchrotron COSY. The obtained cross section as well as an upper limit at an excess energy of Q = 3 MeV represent the first measurements on the K+K- production in the region of small excess energies where production via the channel pp --> pp Phi --> ppK+K- is energetically forbidden. The possible influence of a resonant production via intermediate scalar states f0(980) and a0(980) is discussed., 8 pages, 6 figures, replaced with revised version, accepted for publication in Phys. Lett. B

The near threshold total cross section and angular distributions of K+K− pair production via the reaction pp→ppK+K− have been studied at an excess energy of Q=17 MeV using the COSY-11 facility at the cooler synchrotron COSY. The obtained cross section as well as an upper limit at an excess energy of Q=3 MeV represent the first measurements on the K+K− production in the region of small excess energies where production via the channel pp→ppΦ→ppK+K− is energetically forbidden.

The PINTEX experimental apparatus used for detection of pp→ppπ0 and pp→pnπ+ at IUCF is described. Measured spin observables, integrated as well as angle-or energy-dependent, are compared with the Julich model. Significant discrepancies are found for the angular distributions.

Close-to-threshold data on the elementary kaon and antikaon production channels in the proton-proton interaction have been taken using the COSY-11 installation at the cooler synchrotron COSY Julich. The experimental technique applied at the internal COSY-11 facility—designed for meson production studies at small excess energies—is outlined. The threshold excitation functions for the kaon-hyperon production via the reactions pp→pK+Λ and pp→pK+Σ0 are presented. The magnitude of the production amplitudes is compared at equal excess energies and physical implications of the observed Σ0 suppression in the threshold region are discussed. In addition, within a Dalitz plot analysis the spin-averaged S-wave scattering parameters could be extracted for the Λ-p channel. With the possibility of detecting all final state particles the elementary antikaon production in the reaction pp→ppK+K− has been investigated. Results on the exclusive total cross section fix the scale of the strangeness dissociation into two kaons.

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.

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 .