Quark States Research Articles

Inside the SU(3) quark-antiquark QCD flux tube: Screening versus quantum widening

In lattice QCD, colour confinement manifests in flux tubes. We compute in detail the quark-antiquark flux tube for pure gauge SU(3) dimension $D=3+1$ for quark-antiquark distances R ranging from 0.4 fm to 1.4 fm. To increase the signal over noise ratio, we apply the improved multihit and extended smearing techniques. We detail the gauge invariant squared components of the colour electric and colour magnetic fields both in the mediator plane between the static quark and static antiquark and in the planes of the sources. We fit the field densities with appropriate ansatze and we observe the screening of the colour fields in all studied planes together with the quantum widening of the flux tube in the mediator plane. All components squared of the colour fields are non-vanishing and are consistent with a penetration length lambda ~ 0.22 to 0.24 fm and an effective screening mass mu ~ 0.9 to 0.8 GeV. The quantum widening of the flux tube is well fitted with a logarithmic law in R.

Use ofB→J/ψf0Decays to Discern theqq¯or Tetraquark Nature of Scalar Mesons

We consider the relative decay rates of B(0) and Bs(0) mesons into a J/ψ plus a light scalar meson, either the f0(500) (σ) or the f0(980). We show that it is possible to distinguish between the quark content of the scalars being quark-antiquark or tetraquark by measuring specific ratios of decay rates. Using current data we determine the ratio of form factors in Bs(0)→J/ψf0(980) with respect to B(0)→J/ψf0(500) decays to be 0.99(-0.04)(+0.13) at a four-momentum transfer squared equal to the mass of the J/ψ meson squared. In the case where these light mesons are considered to be quark-antiquark states, we give a determination of the mixing angle between strange and light quark states of less than 29° at 90% confidence level. We also discuss the use of a similar ratio to investigate the structure of other isospin singlet states.

Holographic quark–antiquark potential in hot, anisotropic Yang–Mills plasma

Using the gauge/gravity duality we calculate the heavy quark–antiquark potential in a hot, anisotropic and strongly coupled Yang–Mills plasma in (3+1)-dimensions. As the anisotropic medium we take a deformed version of N=4 super Yang–Mills theory at finite temperature following a recent work where the dual type IIB supergravity solution is also proposed. We turn on a small value of the anisotropy parameter, for which the gravity dual is known analytically (perturbatively), and compute the velocity-dependent quark–antiquark interaction potential when the pair is moving through the plasma with a velocity v. By setting v=0 we recover the static quark–antiquark potential. We numerically study how the potential is modified in the presence of anisotropy. We further show numerically how the quark–antiquark separation (both in the static and the velocity-dependent case) and hence, the screening length gets modified by anisotropy. We discuss various cases depending upon the direction of the dipole and the direction of its propagation and make a comparative study of these cases. We are also able to obtain an analytical expression for the screening length of the dipole moving in a hot, anisotropic plasma in a special case.

Femtoscopy of identified particles at STAR

We present new measurements of $\Lambda-\Lambda$ correlations, which are closely related to $H$-dibaryon: a six quark state predicted by Jaffe (1977), in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV from the STAR experiment. Fits to different potential models are discussed and extracted scattering length and effective range are also presented.We also present spherical harmonic decomposition of pion-kaon correlation function for 0-5% centrality in Au+Au collision at $\sqrt{s_{NN}} = 200$ GeV. In addition, we also discuss results from azimuthal HBT for beam energies 7.7-200 GeV.

Static quark correlators and quarkonium properties at non-zero temperature

We discuss different static quark correlators, including Wilson loops in 2+1 flavor QCD at non-zero temperature and their relation to in-medium quarkonium properties. We present lattice results on static correlation functions obtained with highly improved staggered fermion action and their implications for potential models.

Revisit to non-decoupling MSSM

Dipole operator s¯σμνFμνb requires the helicity flip in the involving quark states thus the breaking of chiral U(3)Q×U(3)d. On the other hand, the b quark mass generation is also a consequence of chiral U(3)Q×U(3)d symmetry breaking. Therefore, in many models, there might be strong correlation between the b→sγ and b quark Yukawa coupling. In this Letter, we use non-decoupling MSSM model to illustrate this feature. In the scenario, the light Higgs boson may evade the direct search experiments at LEPII or Tevatron while the 125 GeV Higgs-like boson is identified as the heavy Higgs boson in the spectrum. A light charged Higgs is close to the heavy Higgs boson which is of 125 GeV and its contribution to b→sγ requires large supersymmetric correction with large PQ and R-symmetry breaking. The large supersymmetric contribution at the same time significantly modifies the b quark Yukawa coupling. With combined flavor constraints B→Xsγ and Bs→μ+μ− and direct constraints on Higgs properties, we find best fit scenarios with light stop of O(500 GeV), negative At around −750 GeV and large μ-term of 2–3 TeV. In addition, reduction in bb¯ partial width may also result in large enhancement of ττ decay branching fraction. Large parameter region in the survival space under all bounds may be further constrained by H→ττ if no excess of ττ is confirmed at LHC. We only identify a small parameter region with significant H→hh decay that is consistent with all bounds and reduced ττ decay branching fraction. In the end, if current dark matter mostly consists of neutralino, direct detection experiments like XENON100 also puts stringent bound over this scenario with light Higgs bosons. The light stops which are required by flavor constraints can further enhance the scattering cross section.

E6inspired supersymmetric models with exact custodial symmetry

The breakdown of E_6 gauge symmetry at high energies may lead to supersymmetric (SUSY) models based on the Standard Model (SM) gauge group together with extra U(1)_{\psi} and U(1)_{\chi} gauge symmetries. To ensure anomaly cancellation the particle content of these E_6 inspired models involves extra exotic states that generically give rise to non-diagonal flavour transitions and rapid proton decay. We argue that a single discrete \tilde{Z}^{H}_2 symmetry can be used to forbid tree-level flavor-changing transitions, as well as the most dangerous baryon and lepton number violating operators. We present 5D and 6D orbifold GUT constructions that lead to the E_6 inspired SUSY models of this type. The breakdown of U(1)_{\psi} and U(1)_{\chi} gauge symmetries that preserves E_6 matter parity assignment guarantees that ordinary quarks and leptons and their superpartners, as well as the exotic states which originate from 27 representations of E_6 survive to low energies. These E_6 inspired models contain two dark-matter candidates and must also include additional TeV scale vectorlike lepton or vectorlike down type quark states to render the lightest exotic quark unstable. We examine gauge coupling unification in these models and discuss their implications for collider phenomenology and cosmology.

Study of ΛΛ correlations and search for H-dibaryon with STAR detector at RHIC

The production of large number of multi-strange hyperons per central nucleus–nucleus collision at RHIC allows us to study hyperon–hyperon interactions through measurement of two particle correlation and search for exotic particles like H-dibaryons. In this article, we discuss analysis details for the measurement of ΛΛ correlation in Au+Au collisions at sNN=200GeV. Fits to different potential models are discussed and the extracted scattering length and effective range are also presented. Finally, we report the progress in searching for the H-dibaryon, a six quark state Jaffe (1977) [1], using its weak decay Λpπ from Au+Au collisions at sNN=200GeV.

Recent Results in Bottomonium

Great strides have been made in the understanding of bound states of the bottom quark, b, and its antiquark, [Formula: see text], since the discovery of the first Ψ resonances in 1977. These bound states, known as bottomonium, have a rich spectrum whose masses and transition amplitudes shed valuable light on the strong interactions. We review some recent developments in bottomonium physics, including the discovery of the spin-singlet states [Formula: see text] and [Formula: see text], the first D-wave states, one or more candidates for spin-triplet [Formula: see text] excitations, and above-threshold states with strong transitions to states below threshold. We also present information about transitions, production, and signatures of new physics.

The horn, kink and step, dale: from few GeV to few TeV

Abstract Rich experimental data have been collected in heavy-ion collisions at high energies to study the properties of strongly interacting matter. As the theory of strong interactions, QCD, predicts asymptotic freedom, the created matter at sufficiently high temperature and density will be dominated by a state of quasi-free quarks and gluons referred to as the Quark-Qluon Plasma (QGP). Experimental signals for the onset of the QGP creation (the onset of the deconfinement) have been predicted within the statistical model for the early stage of nucleus-nucleus collisions. In this model the existence of two different phases is assumed: confined mater and the QGP, as well as a first order phase transition between them. Until recently, these predictions were confirmed only by the NA49 experiment at the CERN SPS. In this report recent results from STAR at RHIC/BNL and from ALICE at LHC/CERN, related to the onset of deconfinement, will be compared to published results from NA49.

Antideuterons from dark matter annihilations and hadronization model dependence

We calculate the antideuteron yield in dark matter annihilations on an event-by-event basis using the HERWIG++ Monte Carlo generator. We present the resulting antideuteron fluxes for quark and gauge boson final states. As deuteron production in the coalescence model depends on momentum differences between nucleons that are small compared to \Lambda_{QCD}, it is potentially very sensitive to the hadronization model employed. We therefore compare our antideuteron yields to earlier results based on PYTHIA, thereby estimating their uncertainties. We also briefly discuss the importance of n>2 final states for annihilations of heavy DM particles.

Application of Fixed Scale Approach to Static Quark Free Energies in Quenched and 2 + 1 Flavor Lattice QCD with Improved Wilson Quark Action

Free energies between static quarks and Debye screening masses in the quark-gluon plasma are studied on the basis of Polyakov-line correlations in lattice simulations of 2+1 flavors QCD with the renormalization-group improved gluon action and the $O(a)$-improved Wilson quark action. We perform simulations at $m_{\rm PS}/m_{\rm V} = 0.63$ (0.74) for light (strange) flavors with lattice sizes of $32^3 \times N_t$ with $N_t=4$--12. We adopt the fixed-scale approach, where temperature can be varied without changing the spatial volume and renormalization factor. We find that, at short distance, the free energies of static quarks in color-singlet channel converge to the static-quark potential evaluated from the Wilson-loop at zero-temperature, in accordance with the expected insensitivity of short distance physics to the temperature. At long distance, the free energies of static quarks approach to twice the single-quark free energies, implying that the interaction between static quarks is fully screened. The screening properties can be well described by the screened Coulomb form with appropriate Casimir factor at high temperature. We also discuss a limitation of the fixed-scale approach at high temperature.

Ultraheavy Yukawa-bound states of fourth-generation at Large Hadron Collider

We present our study of bound states of the fourth generation quarks in the range of 500 to 700 GeV,where we expect binding energies are mainly of Yukawa origin, with QCD subdominant. Near degeneracy of their masses exhibits a new "isospin". We find the most interesting is the production of a color octet, isosinglet vector meson via $q\bar q \to \omega_8$. Its leading decay modes are $\pi_8^\pm W^\mp$, $\pi_8^0Z^0$, and constituent quark decay, with $q\bar q$ and $t\bar t'$ and $b\bar b'$ subdominant. The color octet, isovector pseudoscalar $\pi_8$ meson decays via constituent quark decay, or to $Wg$. This work calls for more detailed study of 4th generation phenomena at LHC.

Test of the OZI rule in vector meson production with the COMPASS experiment

The COMPASS experiment at CERN collected a large set of data with hadron beams (p, π K) and different targets (H2, Pb, Ni, W) in the years 2008 and 2009. The main goal is the search for exotic bound states of quarks and gluons (glueballs, hybrids) and several preliminary results from the ongoing analysis have already emerged.The production of exotic states is known to be favoured in glue-rich environments, e.g. so-called OZI-forbidden processes. The Okubo-Zweig-Iizuka (OZI) rule states that processes with disconnected quark line diagrams are suppressed. As a consequence, states with an ss̄ component should be suppressed with respect to states containing mainly u and d quarks. The numerous reported violations of the OZI rule show that the underlying physics is more complicated. By studying the degree of OZI violation a lot can learned about the production mechanism and possibly also about the nucleon structure itself. The uniquely large COMPASS data sample allows for detailed studies with respect to kinematic variables (e.g. xF). Results from the ongoing analysis on the comparison of ω and ϕ vector mesons production in pp → pp (ω/ϕ) are presented and an outlook on the prospect of spin alignment measurements with COMPASS is given.

Holographic models and the QCD trace anomaly

Five dimensional dilaton models are considered as possible holographic duals of the pure gauge QCD vacuum. In the framework of these models, the QCD trace anomaly equation is considered. Each quantity appearing in that equation is computed by holographic means. Two exact solutions for different dilaton potentials corresponding to perturbative and non-perturbative beta-functions are studied. It is shown that in the perturbative case, where the beta-function is the QCD one at leading order, the resulting space is not asymptotically AdS. In the non-perturbative case, the model considered presents confinement of static quarks and leads to a non-vanishing gluon condensate, although it does not correspond to an asymptotically free theory. In both cases analyses based on the trace anomaly and on Wilson loops are carried out.

Nucleon structure including high Fock states in AdS/QCD

We present a detailed analysis of nucleon electromagnetic and axial form factors in a holographic soft-wall model. This approach is based on an action which describes hadrons with broken conformal invariance and incorporates confinement through the presence of a background dilaton field.For Nc=3 we describe the nucleon structure in a superposition of a three valence quark state with high Fock states including an adjustable number of partons (quarks, antiquarks and gluons) via studying the dynamics of 5D fermion fields of different scaling dimension in anti-de Sitter (ADS) space. According to the gauge/gravity duality the 5D fermion fields of different scaling dimension correspond to the Fock state components with a specific number of partons. In the present application we restrict to the contribution of 3, 4 and 5 parton components in the nucleon Fock state. With a minimal number of free parameters (dilaton scale parameter, mixing parameters of partial contributions of Fock states, coupling constants in the effective Lagrangian) we achieve a reasonable agreement with data for the nucleon form factors.

INTERNAL SYMMETRY GROUPS OF CUBIC ALGEBRAS

We investigate certain Z3-graded associative algebras with cubic Z3 invariant constitutive relations, introduced by one of us some time ago. The invariant forms on finite algebras of this type are given in the cases with two and three generators. We show how the Lorentz symmetry represented by the SL (2, C) group can be introduced without any notion of metric, just as the symmetry of Z3-graded cubic algebra and its constitutive relations. Its representation is found in terms of the Pauli matrices. The relationship of such algebraic constructions with quark states is also considered.

Making confining strings out of mesons

The light mesons such as $\ensuremath{\pi}$, $\ensuremath{\rho}$, $\ensuremath{\omega}$, ${f}_{0}$, and ${a}_{0}$ are possible candidates of magnetic degrees of freedom, if a magnetic dual picture of QCD exists. We construct a linear sigma model to describe spontaneous breaking of the magnetic gauge group, in which there is a stable vortex configuration of vector and scalar mesons. We numerically examine whether such a string can be interpreted as the confining string. By using meson masses and couplings as inputs, we calculate the tension of the string as well as the strength of the Coulomb force between static quarks. They are found to be consistent with those inferred from the quarkonium spectrum and the Regge trajectories of hadrons. By using the same Lagrangian, the critical temperature of the QCD phase transition is estimated, and a nontrivial flavor dependence is predicted. We also discuss a possible connection between the Seiberg duality and the magnetic model we studied.

Running mass, effective energy, and confinement: The lattice quark propagator in Coulomb gauge

We calculate the lattice quark propagator in Coulomb gauge both from dynamical and quenched configurations. We show that in the continuum limit both the static and full quark propagator are multiplicatively renormalizable. From the propagator we extract the quark renormalization function Z(|p|) and the running mass M(|p|) and extrapolate the latter to the chiral limit. We find that M(|p|) practically coincides with the corresponding Landau gauge function for small momenta. The computation of M(|p|) can be however made more efficient in Coulomb gauge; this can lead to a better determination of the chiral mass and the quark anomalous dimension. Moreover from the structure of the full propagator we can read off an expression for the dispersion relation of quarks, compatible with an IR divergent effective energy. If confirmed on larger volumes this finding would allow to extend the Gribov-Zwanziger confinement mechanism to the fermionic sector of QCD.

Variational study of the flux tube recombination in the two quarks and two antiquarks system in lattice QCD

The color fields in a system composed by two static quarks and two static antiquarks are studied. We use a variational method, to probe not only the ground state but also the first excited state. These results permit us to observe and interpret the flux tube recombination in the mesons-to-mesons and the tetraquark-to-mesons transitions, for both states. The results are compared with previous results for the static potential and the Casimir scaling predictions.