Exploring early parton momentum distribution with the ridge from the near-side jet
In a central nucleus-nucleus collision at high energies, medium partons kicked by a near-side jet acquire a momentum along the jet direction and subsequently materialize as the observed ridge particles. They carry direct information on the early parton momentum distribution which can be extracted by using the ridge data for central AuAu collisions at √s NN = 200 GeV. The extracted parton momentum distribution has a thermal-like transverse momentum distribution but a non-Gaussian, relatively flat rapidity distribution at mid-rapidity with sharp kinematic boundaries at large rapidities that depend on the transverse momentum.

title: Tests of two-body Dirac equation wave functions in the decays of quarkonium and positronium into two photons
abstract: Two-body Dirac equations of constraint dynamics provide a covariant framework to investigate the problem of highly relativistic quarks in meson bound states. This formalism eliminates automatically the problems of relative time and energy, leading to a covariant three dimensional formalism with the same number of degrees of freedom as appears in the corresponding nonrelativistic problem. It provides bound state wave equations with the simplicity of the nonrelativistic Schr\"odinger equation. Here we begin important tests of the relativistic 16 component wave function solutions obtained in a recent work on meson spectroscopy, extending a method developed previously for positronium decay into two photons. Preliminary to this we examine the positronium decay in the $^{3}P_{0,2}$ states as well as the $^{1}S_{0}$. The two-gamma quarkonium decays that we investigate are for the ${\ensuremath{\eta}}_{c}$, ${\ensuremath{\eta}}_{c}^{\ensuremath{'}}$, ${\ensuremath{\chi}}_{c0}$, ${\ensuremath{\chi}}_{c2}$, ${\ensuremath{\pi}}^{0}$, ${\ensuremath{\pi}}_{2}$, ${a}_{2}$, and ${f}_{2}^{\ensuremath{'}}$ mesons. Our results for the four charmonium states compare well with those from other quark models and show the particular importance of including all components of the wave function as well as strong and c.m. energy dependent potential effects on the norm and amplitude. The results for the ${\ensuremath{\pi}}^{0}$, although off the experimental rate by 13%, are much closer than the usual expectations from a potential model. We conclude that the two-body Dirac equations lead to wave functions which provide good descriptions of the two-gamma decay amplitude and can be used with some confidence for other purposes.

title: Extended Glauber Model of Antiproton-Nucleus Annihilation for All Energies and Mass Numbers
abstract: Previous analytical formulas in the Glauber model for high-energy nucleus-nucleus collisions developed by Wong are utilized and extended to study Antiproton-nucleus annihilations for both high and low energies, after taking into account the effects of Coulomb and nuclear interactions, and the change of the antiproton momentum inside a nucleus. The extended analytical formulas capture the main features of the experimental antiproton-nucleus annihilation cross sections for all energies and mass numbers. At high antiproton energies, they exhibit the granular property for the lightest nuclei and the black-disk limit for the heavy nuclei. At low antiproton energies, they display the effect of the antiproton momentum increase due to the nuclear interaction for the light nuclei, and the effect of the magnification due to the attractive Coulomb interaction for the heavy nuclei.

title: Potential Models and Lattice Gauge Current-Current Correlators
abstract: We compare current-current correlators in lattice gauge calculations with correlators in different potential models for a pseudoscalar charmonium in the quark-gluon plasma. An important ingredient in the evaluation of the current-current correlator in the potential model is the basic principle that, out of the set of continuum states, only resonance states and Gamow states with lifetimes of sufficient magnitudes can propagate as composite objects and can contribute to the current-current correlator. When the contributions from the bound states and continuum states are properly treated, the potential model current-current correlators obtained with the potential proposed by Wong [ (2005)] are consistent with the lattice gauge correlators. The proposed potential model thus gains support to be a useful tool to complement lattice gauge calculations for the study of QQ{bar} states at high temperatures.

title: Singularity structures in Coulomb-type potentials in two-body Dirac equations of constraint dynamics
abstract: Two-body Dirac equations (TBDE) of Dirac's relativistic constraint dynamics have been successfully applied to obtain a covariant nonperturbative description of QED and QCD bound states. Coulomb-type potentials in these applications lead naively in other approaches to singular relativistic corrections at short distances that require the introduction of either perturbative treatments or smoothing parameters. We examine the corresponding singular structures in the effective potentials of the relativistic Schroedinger equation obtained from the Pauli reduction of the TBDE. We find that the relativistic Schroedinger equation leads in fact to well-behaved wave function solutions when the full potential and couplings of the system are taken into account. The most unusual case is the coupled triplet system with S=1 and L={l_brace}(J-1),(J+1){r_brace}. Without the inclusion of the tensor coupling, the effective S-state potential would become attractively singular. We show how including the tensor coupling is essential in order that the wave functions be well-behaved at short distances. For example, the S-state wave function becomes simply proportional to the D-state wave function and dips sharply to zero at the origin, unlike the usual S-state wave functions. Furthermore, this behavior is similar in both QED and QCD, independent of the asymptotic freedom behavior of the assumed QCDmore » vector potential. Light- and heavy-quark meson states can be described well by using a simplified linear-plus-Coulomb-type QCD potential apportioned appropriately between world scalar and vector potentials. We use this potential to exhibit explicitly the origin of the large pi-rho splitting and effective chiral symmetry breaking. The TBDE formalism developed here may be used to study quarkonia in quark-gluon plasma environments.« less

title: Quantum Treatment of the Multiple Scattering and Collective Flow in Intensity Interferometry
abstract: We apply the path‐integral method to study the multiple scattering and collective flow in intensity interferometry in high‐energy heavy‐ion collisions. We show that the Glauber model and eikonal approximation in an earlier quantum treatment are special examples of the more general path‐integral method. The multiple scattering and collective flow lead essentially to an initial source at a shifted momentum, with a multiple collision absorption factor that depends on the pion absorption cross section and a phase factor that depends on the deviations of the in‐medium particle momenta from their asymptotic values.

title: Multi‐hadron states in Lattice QCD spectroscopy
abstract: The ability to reliably measure the energy of an excited hadron in Lattice QCD simulations hinges on the accurate determination of all lower‐lying energies in the same symmetry channel. These include not only single‐particle energies, but also the energies of multi‐hadron states. This talk deals with the determination of multi‐hadron energies in Lattice QCD. The group‐theoretical derivation of lattice interpolating operators that couple optimally to multi‐hadron states is described. We briefly discuss recent algorithmic developments which allow for the efficient implementation of these operators in software, and present numerical results from the Hadron Spectrum Collaboration.

title: Excited isovector mesons using the stochastic LapH method
abstract: The spectrum of excited isovector mesons is studied using a 32^3 x 256 anisotropic lattice with u,d quark masses set to give a pion mass near 240 MeV. Results in the bosonic isovector nonstrange symmetry channels of zero total momentum are presented using correlation matrices of unprecedented size. In addition to spatially-extended single-meson operators, large numbers of two-meson operators are used, involving a wide variety of light isovector, isoscalar, and strange meson operators of varying relative momenta. All needed Wick contractions are efficiently evaluated using a stochastic method of treating the low-lying modes of quark propagation that exploits Laplacian Heaviside quark-field smearing. Level identification is discussed.

title: Progress Report on Computing Excited‐State Hadron Masses in Lattice QCD
abstract: Our progress in computing the spectrum of excited baryons and mesons in lattice QCD is described. Sets of spatially‐extended hadron operators with a variety of different momenta are used. A new method of stochastically estimating the low‐lying effects of quark propagation is utilized which allows reliable determinations of temporal correlations of both single‐hadron and multi‐hadron operators. The method is tested on the isoscalar mesons in the scalar, pseudoscalar, and vector channels, and on the two‐pion system of total isospin I = 0,1,2.

title: Extended hadron and two-hadron operators of definite momentum for spectrum calculations in lattice QCD
abstract: Multi-hadron operators are crucial for reliably extracting the masses of excited states lying above multi-hadron thresholds in lattice QCD Monte Carlo calculations. The construction of multi-hadron operators with significant coupling to the lowest-lying multi-hadron states of interest involves combining single hadron operators of various momenta. The design and implementation of large sets of spatially-extended single-hadron operators of definite momentum and their combinations into two-hadron operators are described. The single hadron operators are all assemblages of gauge-covariantly-displaced, smeared quark fields. Group-theoretical projections onto the irreducible representations of the symmetry group of a cubic spatial lattice are used in all isospin channels. Tests of these operators on 24^3 x 128 and 32^3 x 256 anisotropic lattices using a stochastic method of treating the low-lying modes of quark propagation which exploits Laplacian Heaviside quark-field smearing are presented. The method provides reliable estimates of all needed correlations, even those that are particularly difficult to compute, such as eta eta -> eta eta in the scalar channel, which involves the subtraction of a large vacuum expectation value. A new glueball operator is introduced, and the evaluation of the mixing of this glueball operator with a quark-antiquark operator, pi-pi, and eta-eta operators is shown to be feasible.

title: The running coupling of 8 flavors and 3 colors
abstract: A bstractWe compute the renormalized running coupling of SU(3) gauge theory coupled to Nf = 8 flavors of massless fundamental Dirac fermions. The recently proposed finite volume gradient flow scheme is used. The calculations are performed at several lattice spacings allowing for a controlled continuum extrapolation. The results for the discrete β-function show that it is monotonic without any sign of a fixed point in the range of couplings we cover. As a cross check the continuum results are compared with the well-known perturbative continuum β-function for small values of the renormalized coupling and perfect agreement is found.