Polarization phenomena in the reaction NN to NNpi near threshold

First calculations for spin-dependent observables of the reactions $pp \to pp\pi^0$, $pp \to pn\pi^+$ and $pp \to d\pi^+$ near threshold are presented, employing the J\"ulich model for pion production. The influence of resonant (via the excitation of the $\Delta (1232)$) and non-resonant p-wave pion production mechanisms on these observables is examined. For the reactions $pp \to pn\pi^+$ and $pp \to d\pi^+$ nice agreement of our predictions with the presently available data on spin correlation coefficents is observed whereas for $pp \to pp\pi^0$ the description of the data is less satisfying.Comment: 10 pages, 4 figure

Heavy Meson Production in NN Collisions with Polarized Beam and Target -- A new facility for COSY

The study of near--threshold meson production in pp and pd collisions involving polarized beams and polarized targets offers the rare opportunity to gain insight into short--range features of the nucleon--nucleon interaction. The Cooler Synchrotron COSY at FZ--J\"ulich is a unique environment to perform such studies. Measurements of polarization observables require a cylindrically symmetrical detector, capable to measure the momenta and the directions of outgoing charged hadrons. The wide energy range of COSY leads to momenta of outgoing protons to be detected in a single meson production reaction between 300 and 2500 MeV/c. Scattering angles of protons to be covered extend to about $45^{\circ}$ in the laboratory system. An azimuthal angular coverage of the device around 98% seems technically achievable. The required magnetic spectrometer could consist of a superconducting toroid, providing fields around 3 T.Comment: 6 pages, 1 figure, submitted to Czechoslovak Journal of Physic

Measurement of Partial-Wave Contributions in pp --> pp pi^0

We report a measurement of the spin-dependent total cross section ratios delta_sigma_T/sigma_tot and delta_sigma_L/sigma_tot of the pp --> pp pi^0 reaction between 325 MeV and 400 MeV. The experiment was carried out with a polarized internal target in a storage ring. Non-vertical beam polarization was obtained by the use of solenoidal spin rotators. Near threshold, the knowledge of both spin-dependent total cross sections is sufficient to deduce the strength of certain participating partial waves, free of any model.Comment: 6 pages, 4 figure

Coarse Graining of Nonbonded Inter-particle Potentials Using Automatic Simplex Optimization to Fit Structural Properties

We implemented a coarse-graining procedure to construct mesoscopic models of complex molecules. The final aim is to obtain better results on properties depending on slow modes of the molecules. Therefore the number of particles considered in molecular dynamics simulations is reduced while conserving as many properties of the original substance as possible. We address the problem of finding nonbonded interaction parameters which reproduce structural properties from experiment or atomistic simulations. The approach consists of optimizing automatically nonbonded parameters using the simplex algorithm to fit structural properties like the radial distribution function as target functions. Moreover, any mix of structural and thermodynamic properties can be included in the target function. Different spherically symmetric inter-particle potentials are discussed. Besides demonstrating the method for Lennard--Jones liquids, it is applied to several more complex molecular liquids such as diphenyl carbonate, tetrahydrofurane, and monomers of poly(isoprene).Comment: 24 pages, 3 tables, 14 figures submitted to the Journal of Chemical Physics (JCP