A study of gluon scattering and gluon fragmentation in highp T interactions at the ISR

Gluon scattering processes are studied in hadronic highp _T events using data obtained with the Split Field Magnet detector (SFM) at the CERN ISR. The experimental set-up allowed the scanning of a wide range of parton energies and scattering angles. It is shown that for positive pions as trigger particles, the parton composition of the recoil jet is correlated with the polar angle and transverse momentum of the triggering pion. Over the kinematical region studied, the recoil jet originates predominantly from scatered gluons, with an increasing prevalence of the gluon component towards forward triggering angles. The variation of the momentum structure of the recoil jet with the trigger angle indicates that the fragmentation function of gluons is softer than that of quarks.     

State space calculations for discrete probability densities

State space methods have proved to be powerful theoretical and computational tools in a number of areas of applications, in particular filtering and control theory. In this paper we advocate the use of state space methods for the study of discrete probability densities on the set {0,1,2,…}. The fundamental approach is to consider the class of all discrete probability densities that can be represented as the impulse response/convolution kernel of a finite dimensional discrete time state space system. We show that all standard operations such as the calculation of moments, convolution, scaling, translation, product, etc. can be carried out using system representations.     

On models of polydisperse sedimentation with particle-size-specific hindered-settling factors

Polydisperse suspensions consist of particles differing in size or density that are dispersed in a viscous fluid. During sedimentation, the different particle species segregate and create areas of different composition. Spatially one-dimensional mathematical models of this process can be expressed as strongly coupled, nonlinear systems of first-order conservation laws. The solution of this system is the vector of volume fractions of each species as a function of depth and time, which will in general be discontinuous. It is well known that this system is strictly hyperbolic provided that the Masliyah–Lockett–Bassoon (MLB) flux vector is chosen, the particles have the same density, and the hindered-settling factor (a multiplicative algebraic expression appearing in the flux vector) does not depend on the particle size but is the same for all species. It is the purpose of this paper to prove that this hyperbolicity result remains valid in a fairly general class of cases where the hindered-settling factor does depend on particle size. This includes the common power-law type hindered-settling factor in which the exponent, sometimes called Richardson–Zaki exponent, is determined individually for each species, and is a decreasing function of particle size. The importance of this paper is two-fold: it proves stability for a class of polydisperse suspensions that was not covered in previous work, and it offers a new analysis of real data.     

Comparative study of baryon production in hard and soft processes

The production ratios of baryons and mesons in deep inelastic reactions are compared with the corresponding quantities in soft hadronic interactions. Contrary to general believe these ratios are equal within the experimental uncertainties and show the same dependence on the longitudinal momentum, provided that processes are compared, where a fixed number of valence quarks is common to the initial state and the secondary under consideration, i.e. processes which are equivalent in the sense of quark recombination mechanisms.     

The hadronic cross section of electron-positron annihilation at 9.5 GeV and the ϒ and ϒ′ resonance parameters

The reaction e⁺e^?→ hadrons has been measured in the ? and ?′ region using the DASP detector at the DESY storage ring DORIS. The following final results are obtained: R_had(9.5 GeV)=3.73±0.16±0.28, Γ_ee(?)=(1.23 ± 0.08 ± 0.12) keV, B_μμ(?)=(3.2±1.3±0.3)%, $\text{Γ}{}_{\mathrm{<mtext>ee</mtext>}}\text{Γ}{}_{\mathrm{<mtext>had</mtext>}}\text{Γ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(?′)=(0.55±0.11 ±0.06)}\text{keV}$, and M(?′)?M(?)=(556 ±10) MeV.     

Electronic structure of CrAs and FeAs

As in a recent study for MnAs a two centre tight binding model consisting of itinerant metal d-states hybridizing with non-metal p-states was applied for CrAs and FeAs to calculate unpolarized and spin polarized local densities of states, ferromagnetic moments and band energies. The factor for the change of the d-band width relative to MnAs was estimated to be 1.3 for CrAs and 0.8 for FeAs. The self-consistent separation of the p- and d-band centres amounts to -1.3 eV for CrAs and -0.5 eV for FeAs providing a charge transfer of 0.8 and 0.6 electrons from the metal to the As atoms, correspondingly. One B8₁ structure and two B31 structures according to low and high temperature phases were studied for each compound. For CrAs self-consistent magnetic moments of 1.58 and 1.2μ_B were obtained, respectively. For FeAs no ferromagnetic moment could be stabilized unless the d-band width was substantially reduced. The results are discussed with respect to MnAs. The model is able to reproduce the increase and breakdown of the magnetic moment for the series CrAs-MnAs-FeAs. Furthermore, the correct structural trend B31-B8₁-B31 is obtained if the band energy differences are corrected by a constant of 0.3 eV. This correction is attributed to the failure of the model to provide absolute differences of total energies.     

Structural and electronic properties of Danzer's model of a three-dimensional quasicrystal

By using deflation rules, the coordinates of the atoms in Danzer's model of a 3d quasicrystal are computed. The resulting atomic positions in a cut through the model well agree with experimental findings. Furthermore, for Danzer's model the static structure factor, the pair correlation function, and properties of a tight binding electron model are studied. The electron density of states shows a characteristic peak at energyE=O, which may be associated to confined states.