71,248 research outputs found

    Vector-to-Pseudoscalar and Meson-to-Baryon Ratios in Hadronic Z Decays at LEP

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    Mass dependences of the total production rates per hadronic Z decay of all light-flavour hadrons measured so far at LEP are extrapolated to the zero mass limit (m=0) using phenomenological laws of hadron production related to the spin, isospin, strangeness content and mass of the particles. The vector-to-pseudoscalar and meson-to-baryon ratios at m=0 are found to be: rho^+ / 3 pi^+ = 1.2 +/- 0.3 and pi^+ / p = 2.9 +/- 0.3, in good agreement with the predictions of quark combinatorics.Comment: LaTeX with sprocl.sty; 6 pages with 2 eps-figures; minor Editor's corrections. Talk given at the 30th International Symposium on Multiparticle Dynamics, Tihany, Lake Balaton, Hungary, October 9-15, 2000. To be published in the Proceedings (World Scientific, Singapore

    (Non)Thermal Aspects of Charmonium Production and a New Look at J/ψ\psi Suppression

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    To investigate a recent proposal that J/ψ\psi production in ultra-relativistic nuclear collisions is of thermal origin we have reanalyzed the data from the NA38/50 collaboration within a thermal model including charm. Comparison of the calculated with measured yields demonstrates the non-thermal origin of hidden charm production at SPS energy. However, the ratio ψâ€Č\psi^{'}/(J/ψ)\psi) exhibits, in central nucleus-nucleus collisions, thermal features which lead us to a new interpretation of open charm and charmonium production at SPS energy. Implications for RHIC and LHC energy measurements will be discussed.Comment: 12 pages, 3 eps figures, final version with slight corrections, Phys. Lett. B (in print

    Statistical hadronization of charmed quarks at SPS and RHIC

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    Production of open and hidden charm hadrons in heavy ion collisions is considered within the statistical coalescence model. The charmed quark-antiquark pairs are assumed to be created at the initial stage of the reaction in hard parton collisions. The number of these pairs is conserved during the evolution of the system. At the hadronization stage, the charmed (anti)quarks are distributed among open and hidden charm hadrons in accordance with the laws of statistical mechanics. The model is in agreement with the experimental data on J/psi to Drell-Yan ratio in Pb+Pb collisions at SPS. This agreement can be reached only if a rather strong enhancement of the open charm production in central Pb+Pb collisions is assumed. A possible mechanism of the charm enhancement is discussed. At the top RHIC energy, the model predicts an increase of J/psi to Drell-Yan ratio in more central nucleus-nucleus collisions with respect to less central ones.Comment: Presented at 16th International Conference "Quark Matter", Nantes (France), July 18-24, 2002; 4 pages, LaTeX, 2 PS-figure

    Extended Modified Observable Technique for a Multi-Parametric Trilinear Gauge Coupling Estimation at LEP II

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    This paper describes the extension of the Modified Observables technique in estimating simultaneously more than one Trilinear Gauge Couplings. The optimal properties, unbiasedness and consistent error estimation of this method are demonstrated by Monte Carlo experimentation using â„“Îœjj\ell \nu jj four-fermion final state topologies. Emphasis is given in the determination of the expected sensitivities in estimating the Î»Îłâˆ’Î”g1z\lambda_{\gamma} - \Delta g_{1}^{z} and Δkγ−Δg1z\Delta k_{\gamma} - \Delta g_{1}^{z} pair of couplings with data from the 183 GeV LEPII run.Comment: (17 pages, 8 figures

    Multidimensional Binning Techniques for a Two Parameter Trilinear Gauge Coupling Estimation at LEP II

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    This paper describes two generalization schemes of the Optimal Variables technique in estimating simultaneously two Trilinear Gauge Couplings. The first is an iterative procedure to perform a 2-dimensional fit using the linear terms of the expansion of the probability density function with respect to the corresponding couplings, whilst the second is a clustering method of probability distribution representation in five dimensions. The pair production of W's at 183 GeV center of mass energy, where one W decays leptonically and the other hadronically, was used to demonstrate the optimal properties of the proposed estimation techniques.Comment: (25 pages, 11 figures

    Using a Logic Programming Framework to Control Database Query Dialogues in Natural Language

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    We present a natural language question/answering system to interface the University of Évora databases that uses clarification dialogs in order to clarify user questions. It was developed in an integrated logic programming framework, based on constraint logic programming using the GnuProlog(-cx) language [2,11] and the ISCO framework [1]. The use of this LP framework allows the integration of Prolog-like inference mechanisms with classes and inheritance, constraint solving algorithms and provides the connection with relational databases, such as PostgreSQL. This system focus on the questions’ pragmatic analysis, to handle ambiguity, and on an efficient dialogue mechanism, which is able to place relevant questions to clarify the user intentions in a straightforward manner. Proper Nouns resolution and the pp-attachment problem are also handled. This paper briefly presents this innovative system focusing on its ability to correctly determine the user intention through its dialogue capability

    Multiplicities, fluctuations and correlations

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    The recent results on hadron multiplicities in heavy and light quark fragmentation, multiplicity local fluctuations and multiparticle correlations submitted to the Conference are reviewed.Comment: 5 pages, 4 eps figs. Talk given at the 31st International Conference on High Energy Physics (ICHEP02), Amsterdam, The Netherlands, 24-31 July 2002. To appear in the Proceeding

    Kahler geometry of toric varieties and extremal metrics

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    Recently Guillemin gave an explicit combinatorial way of constructing "toric" Kahler metrics on (symplectic) toric varieties, using only data on the moment polytope. In this paper, differential geometric properties of these metrics are investigated using Guillemin's construction. In particular, a nice combinatorial formula for the scalar curvature is given, and the Euler-Lagrange condition for such "toric" metrics being extremal (in the sense of Calabi) is derived. A construction, due to Calabi, of a 1-parameter family of extremal metrics of non-constant scalar curvature is recast very simply and explicitly. Finally, a curious combinatorial formula for convex polytopes, that follows from the relation between the total integral of the scalar curvature and the wedge product of the first Chern class with a suitable power of the Kahler class, is presented.Comment: 12 pages, submitted to International Journal of Mathematic

    Dual projection in a two-dimensional curved expanding universe

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    It is a well known result that the scalar field is composed of two chiral particles (Floreanini-Jackiw particles) of opposite chiralities. Also, that a Siegel particle spectrum is formed by a nonmover field (a Hull's noton) and a FJ particle. In this work we show that in a scalar field spectrum, in a curved expanding universe scenario, we can find two dynamical chiral fields.Comment: 6 pages, Revtex. Final version to appear in Int. J. Mod. Phys.

    Toric Kahler Metrics: Cohomogeneity One Examples of Constant Scalar Curvature in Action-Angle Coordinates

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    In these notes, after an introduction to toric Kahler geometry, we present Calabi's family of U(n)-invariant extremal Kahler metrics in symplectic action-angle coordinates and show that it actually contains, as particular cases, many interesting cohomogeneity one examples of constant scalar curvature.Comment: 20 pages, 1 figure, for the proceedings of the XI International Conference on Geometry, Integrability and Quantization, Varna, Bulgaria, June 5--10, 200
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