Cross-sections and spin observables in proton-proton elastic scattering: Results from EDDA at COSY

At the Cooler-Synchrotron COSY/Jülich polarized and unpolarized elastic proton-proton scattering has been investigated with the EDDA-Experiment in the energy range ( -2.5 GeV). By taking scattering data during the acceleration of the beam with a large-acceptance ( - ) detector, precise excitation functions for differential cross-section and analyzing power have been measured in small energy steps with consistent normalization with respect to luminosity and polarization. These data have helped to improve the determination of phase-shifts at higher energies and impose tight quantitative upper bounds on possible resonant contributions to pp elastic scattering, as they might arise from exotic 6-quark configurations. Recently, with polarized beam and target, the spin-correlation parameters , , and have been determined at 10 energies between 0.8 and 2.5 GeV. The observable has been measured the first time above 800 MeV and our results are in sharp contrast to phase-shift predictions at higher energies.Received: 30 September 2002, Published online: 22 October 2003PACS: 24.70. + s Polarization phenomena in reactions - 25.40.Cm Elastic proton scattering - 11.80.Et Partial-wave analysis - 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.)     

Differentielle Streuquerschnitte bei der Wechselwirkung neutraler Moleküle

An apparatus to measure differential scattering cross sections using crossed molecular beams is described and results for the scattering of potassium atoms by different heavy atoms and molecules are presented. The experimental data are compared with theoretical calculations for a Buckingham-(exp-six)-potential and the parameters of this potential are determined. To carry out this comparison, it was necessary to average the existing calculations of E. A.Mason over the Maxwellian velocity distribution in the potassium beam. These averaged differential cross sections are tabulated for various angles and temperatures in the appendix of the present paper. Using crossed beams of molecules containing halogens, we can observe chemical reactions. Methods to determine total and differential reaction cross sections are discussed.     

Comparison of measured total integral cross sections for noble gas dimer-atom systems with IOSA calculations

Experimentally determined total integral cross sections for noble gas dimer-atom systems, involving the energetically accessible channels of excitation, exchange and dissociation are compared with theoretical values calculated using a simple formula. This simple formula is derived using the multichannel optical theorem and the infinite order sudden approximation (IOSA). The potential is well approximated by the sum of known pair potentials. Setting the IOSA parameters L and K equal to the angular momentum and the wave number of the initial channel, respectively, the largest error between the experimental and theoretical results is about 10%. We noticed that a proper choice of the relation between K and the collision energy greatly reduces this error; a possible explanation cannot be given.     

Totale Streuquerschnitte für den Stoß von H2, D2 und He an den Edelgasen Ne,Ar, Kr und Xe im thermischen Energiebereich

The velocity dependence of the total elastic cross section has been measured for the scattering of H₂, D₂, and He beams by Ne, Ar, Kr, and Xe gases. Velocity-selected beams were attenuated by gas in a scattering chamber. A universal detector, with a magnetic mass separator, was used in conjunction with lock-in techniques. The results are compared with quantum mechanical calculations using a Lennard-Jones-(12.6)-potential, and employing suitable averaging over experimental velocity distributions. Potential parameters are presented. These are in good agreement with those expected from other methods of measurement.     

A Duality for Spin Verlinde Spaces and Prym Theta Functions

The paper proves canonical isomorphisms between Spin Verlindespaces, that is, spaces of global sections of a determinantline bundle over the moduli space of semistable Spin_n-bundlesover a smooth projective curve C, and the dual spaces of thetafunctions over Prym varieties of unramified double covers ofC.     

The influence of sequential extremal processes on the partial sum process

In this paper we derive general upper bounds for the total variation distance between the distributions of a partial sum process in row-wise independent, non-negative triangular arrays and the sum of a fixed number of corresponding extremal processes. As a special case we receive bounds for the supremum distance between the distribution functions of a partial sum and the sum of corresponding upper extremes which improve upon existing results. The outcome may be interpreted as the influence of large insurance claims on the total loss. Moreover, under an additional infinitesimal condition we also prove explicit bounds for limits of the above quantities. Thereby we give a didactic and elementary proof of the Ferguson–Klass representation of Lévy processes on ?_?≥?0 which reflects the influence of extremal processes in insurance.     

New Poincaré-type inequalities

We present some Poincaré-type inequalities for quadratic matrix fields with applications e.g. in gradient plasticity or fluid dynamics. In particular, applications to the pseudostress–velocity formulation of the stationary Stokes problem and to infinitesimal gradient plasticity are discussed.     

Single-molecule junctions based on nitrile-terminated biphenyls: a promising new anchoring group

We present a combined experimental and theoretical study of the electronic transport through single-molecule junctions based on nitrile-terminated biphenyl derivatives. Using a scanning tunneling microscope-based break-junction technique, we show that the nitrile-terminated compounds give rise to well-defined peaks in the conductance histograms resulting from the high selectivity of the N-Au binding. Ab initio calculations have revealed that the transport takes place through the tail of the LUMO. Furthermore, we have found both theoretically and experimentally that the conductance of the molecular junctions is roughly proportional to the square of the cosine of the torsion angle between the two benzene rings of the biphenyl core, which demonstrates the robustness of this structure-conductance relationship.     

Studies on pyrrolidinones. A convenient synthesis of 5-cyano-2-pyrrolidinone derivatives

The reaction of 2-pyrrolidinone-5-carboxamide (pyroglutamide) with trimethylchlorosilane and zinc chloride as a catalyst afford in one step a 91% yield of N-trimethylsilylpyroglutamic acid nitrile whose acylation gives N-acyl compounds 2b,c .