119274040
Wigner function of produced particles in string fragmentation
I show that quantum chromodynamics in four dimensions (QCD4) with transverse confinement can be approximately compactified into QCD2 with a transverse quark mass m{sub T} that is obtained by solving a set of coupled transverse eigenvalue equations. In the limits of a strong coupling and a large number of flavors, QCD2 further admits Schwinger QED2-type bosonized solutions. I therefore examine phenomenologically the space-time dynamics of particles produced in string fragmentation by studying the Wigner function of bosons produced in Schwinger QED2, which mimics many features of string fragmentation in quantum chromodynamics. I find that particles with momenta in different regions of the rapidity plateau are produced at the initial moment of string fragmentation as a quark pulls away from an antiquark at high energies, in contrast to classical depictions of string fragmentation with longitudinal space-momentum-time ordering.
119111169
Anomalous Soft Photons associated with Hadron Production in String Fragmentation
The bosonized QCD2+QED2 system for quarks with two flavors contains QCD2 and QED2 bound states, with an isoscalar photon at about 25 MeV and an isovector (I = 1,I3 = 0) photon at about 44 MeV. Consequently, when a quark and an antiquark at the two ends of a string pulls apart from each other at high energies, hadrons and soft photons will be produced simultaneously in the fragmentation of the string. The production of the QED2 soft photons in association with hadrons may explain the anomalous soft photon data in hadron‐hadron collisions and e+‐e− annihilations at high energies.
119431536
Meson-meson scattering in relativistic constraint dynamics
Dirac's relativistic constraint dynamics have been successfully applied to obtain a covariant nonperturbative description of QED and QCD bound states. We use this formalism to describe a microscopic theory of meson-meson scattering as a relativistic generalization of the nonrelativistic quark-interchange model developed by Barnes and Swanson.
119115984
Singularity structures in Coulomb-type potentials in two-body Dirac equations of constraint dynamics
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
119205968
The Momentum Kick Model Description of the Near-Side Ridge and Jet Quenching
In central high-energy heavy-ion collisions, jets are produced in nucleon-nucleon collisions and they interact with the dense medium produced in the interacting region. Depending on the relative azimuthal angle relative to the trigger particle, observed high-pt jets can be classified as near-side jets or away-side jets. An away-side jet is associated with a broad cone of particles pointing azimuthally opposite to the trigger particle direction. The strong attenuation of the away-side jet in its passage through the produced dense matter is one of the many notable experimental observations in relativistic heavy-ion collisions and is a signature for the production of the strongly-coupled quark-gluon plasma [1, 2, 3, 4]. On the other hand, a near-side jet is characterized by the presence of associated particles within a narrow azimuthal angle along the trigger particle direction. It retains many of the characteristics of the associated fragmentation products as those of a jet in pp and peripheral heavy-ion collisions. The near-side jet occurs when the high-pt jet emerges near the surface of the produced parton medium.
6746774
Tsallis Fits to p_t Spectra for pp Collisions at LHC
Phenomenological Tsallis fits to the CMS and ATLAS transverse spectra of charged particles were found to extend for pT from 0.5 to 181 GeV in pp collisions at the LHC at sqrt(s) = 7 TeV, and for pT from 0.5 to 31 GeV at sqrt(s) = 0.9 TeV. The simplicity of the Tsallis parametrization and the large range of the fitting transverse momentum raise questions on the physical meaning of the degrees of freedom that enter into the Tsallis distribution or q-statistics
121012194
Can the Higgs Impostor Hide Near the Conformal Window
We present a minimal candidate model for the composite Higgs mechanism with a fermion doublet in the two-index symmetric (sextet) representation of the SU(3) color gauge group. The model is known to be close to the conformal window with a small β-function. Chiral symmetry breaking with vacuum condensate becomes the origin of electroweak symmetry breaking from compositeness. Close to the conformal window, a light scalar state with Higgs quantum numbers is emerging. Associations with the recently observed 126 GeV Higgs boson, or with a dilaton state from broken scale invariance, are subjects of ongoing investigations.
119277308
Excited isovector mesons using the stochastic LapH method
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.
118408634
Applications of the Stochastic LapH Method
University of California, San Diego, CA 92093, U.S.A.E-mail: rickywong@physics.ucsd.eduProgress in computing the hadron spectrum in lattice QCD using stochastic LapH quark propaga-tors is described. The stochastic LapH algorithm is a particular quark smearing algorithm that alsoallows the computation of all-to-all quark propagators. All-to-all quark propagators are requiredin our approach of using a large set of spatially extended hadron operators and explicit multi-particle operators to access excited states. We report on the progress made in the various isospinchannels on 2+1 dynamical, anisotropic lattices generated by the Hadron Spectrum Collaboration.CERN-PH-TH/2013-010The XXX International Symposium on Lattice Field Theory - Lattice2012June 24 - 29, 2012Cairns, Australia
118639009
Multi‐hadron states in Lattice QCD spectroscopy
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.
56105021
Twelve fundamental and two sextet fermion flavors
We report extended simulation results and their new analysis in two important gauge theories with twelve fermion flavors in the fundamental SU(3) color representation and two fermions in the sextet representation. We probe the $N_f=12$ model with respect to the conformal window using mass deformed finite size scaling (FSS) theory driven by the fermion mass anomalous dimension. Our results at fixed gauge coupling show problems with the conformal scenario of the $N_f=12$ model. In the sextet model with two flavors, under the conformal hypothesis, we determine large values for the anomalous fermion mass dimension with $\gamma\geq 1$. Since our sextet analysis favors the chiral symmetry breaking hypothesis without conformality, the large exponent $\gamma$ could play an important role in understanding the composite Higgs mechanism. The new results discussed here include our extended data sets and exceed what was presented at the conference.