An SU(3) model for octet baryon and meson fragmentation

The production of the octet of baryons and mesons in e^+ e^- collisions is analysed, based on considerations of SU(3) symmetry and a simple model for SU(3) symmetry breaking in fragmentation functions. All fragmentation functions, D_q^h(x, Q^2), describing the fragmentation of quarks into a member of the baryon octet (and similarly for fragmentation into members of the meson octet) are expressed in terms of three SU(3) symmetric functions, \alpha(x, Q^2), \beta(x, Q^2), and \gamma(x, Q^2). With the introduction of an SU(3) breaking parameter, \lambda, the model is successful in describing hadroproduction data at the Z pole. The fragmentation functions are then evolved using leading order evolution equations and good fits to currently available data at 34 GeV and at 161 GeV are obtained.Comment: 24 pages LaTeX file including 11 postscript figure file

A New 5 Flavour NLO Analysis and Parametrizations of Parton Distributions of the Real Photon

New, radiatively generated, NLO quark (u,d,s,c,b) and gluon densities in a real, unpolarized photon are presented. We perform three global fits, based on the NLO DGLAP evolution equations for Q^2>1 GeV^2, to all the available structure function F_2^gamma(x,Q^2) data. As in our previous LO analysis we utilize two theoretical approaches. Two models, denoted as FFNS_{CJK}1 & 2 NLO, adopt the so-called Fixed Flavour-Number Scheme for calculation of the heavy-quark contributions to F_2^gamma(x,Q^2), the CJK NLO model applies the ACOT(chi) scheme. We examine the results of our fits by a comparison with the LEP data for the Q^2 dependence of the F_2^gamma, averaged over various x-regions, and the F_2,c^gamma. Grid parametrizations of the parton densities for all fits are provided.Comment: 49 pages, 27 postscript figures; FORTRAN programs available at http://www.fuw.edu.pl/~pjank/param.htm

Pion photoproduction on the nucleon in the quark model

We present a detailed quark-model study of pion photoproduction within the effective Lagrangian approach. Cross sections and single-polarization observables are investigated for the four charge channels, $\gamma p\to \pi^+ n$, $\gamma n\to \pi^- p$, $\gamma p\to \pi^0 p$, and $\gamma n\to \pi^0 n$. Leaving the $\pi N\Delta$ coupling strength to be a free parameter, we obtain a reasonably consistent description of these four channels from threshold to the first resonance region. Within this effective Lagrangian approach, strongly constrainted by the quark model, we consider the issue of double-counting which may occur if additional {\it t}-channel contributions are included.Comment: Revtex, 35 pages, 16 eps figures; version to appear on PR

Photon Structure and Quantum Fluctuation

Photon structure derives from quantum fluctuation in quantum field theory to fermion and anti-fermion, and has been an experimentally established feature of electrodynamics since the discovery of the positron. In hadronic physics, the observation of factorisable photon structure is similarly a fundamental test of the quantum field theory Quantum Chromodynamics (QCD). An overview of measurements of hadronic photon structure in e+e- and ep interactions is presented, and comparison made with theoretical expectation, drawing on the essential features of photon fluctuation into quark and anti-quark in QCD.Comment: 29 pages, 15 figures, to appear in Philosophical Transactions of the Royal Society of London (Series A: Mathematical, Physical and Engineering Sciences

Hadron multiplicities in e+e- annihilation with heavy primary quarks

The multiple hadron production in the events induced by the heavy primary quarks in $e^+e^-$ annihilation is reconsidered with account of corrected experimental data. New value for the multiplicity in $b\bar{b}$ events is presented on the basis of pQCD estimates.Comment: 16 pages, 6 figures. Version accepted for publication in EPJ

Leading particle effect, inelasticity and the connection between average multiplicities in {\bf e+e−e^+e^-} and {\bf pppp} processes

The Regge-Mueller formalism is used to describe the inclusive spectrum of the proton in $p p$ collisions. From such a description the energy dependences of both average inelasticity and leading proton multiplicity are calculated. These quantities are then used to establish the connection between the average charged particle multiplicities measured in {\bf $e^+e^-$} and {\bf $pp/{\bar p}p$} processes. The description obtained for the leading proton cross section implies that Feynman scaling is strongly violated only at the extreme values of $x_F$, that is at the central region ($x_F \approx 0$) and at the diffraction region ($x_F \approx 1$), while it is approximately observed in the intermediate region of the spectrum.Comment: 20 pages, 10 figures, to be published in Physical Review

First-principles calculation of the thermal properties of silver

The thermal properties of silver are calculated within the quasi-harmonic approximation, by using phonon dispersions from density-functional perturbation theory, and the pseudopotential plane-wave method. The resulting free energy provides predictions for the temperature dependence of various quantities such as the equilibrium lattice parameter, the bulk modulus, and the heat capacity. Our results for the thermal properties are in good agreement with available experimental data in a wide range of temperatures. As a by-product, we calculate phonon frequency and Grueneisen parameter dispersion curves which are also in good agreement with experiment.Comment: 9 pages, 8 figures, submitted to Phys. Rev. B April 30, 1998). Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

Clocking hadronization in relativistic heavy ion collisions with balance functions

A novel state of matter has been hypothesized to exist during the early stage of relativistic heavy ion collisions, with normal hadrons not appearing until several fm/c after the start of the reaction. To test this hypothesis, correlations between charges and their associated anticharges are evaluated with the use of balance functions. It is shown that late-stage hadronization is characterized by tightly correlated charge/anticharge pairs when measured as a function of relative rapidity.Comment: 5 pages, 3 figure

An Investigation of Hadronization Mechanism at Z0Z^{0} Factory

We briefly review the hadronization pictures adopted in the LUND String Fragmentation Model(LSFM), Webber Cluster Fragmentation Model(WCFM) and Quark Combination Model(QCM), respectively. Predictions of hadron multiplicity, baryon to meson ratios and baryon-antibaryon flavor correlations, especially related to heavy hadrons at $Z^0$ factory obtained by LSFM and QCM are reported.Comment: 18 pages, 6 figures. accepted by Sci China Phys Mech Astro

Statistical approach for unpolarized fragmentation functions for the octet baryons

A statistical model for the parton distributions in the nucleon has proven its efficiency in the analysis of deep inelastic scattering data, so we propose to extend this approach to the description of unpolarized fragmentation functions for the octet baryons. The characteristics of the model are determined by using some data on the inclusive production of proton and $\Lambda$ in unpolarized deep inelastic scattering and a next-to-leading analysis of the available experimental data on the production of unpolarized octet baryons in $e^+e^-$ annihilation. Our results show that both parton distributions and fragmentation functions are compatible with the statistical approach, in terms of a few free parameters, whose interpretation will be discussed.Comment: 14 pages, 7 eps figures, to appear in Phys. Rev.