Quark States Research Articles

Confinement in a correlated Instanton-Dyon Ensemble

Confinement is a remarkable nonperturbative phenomena emerging from QCD and QCD-like theories. A theoretical understanding of these transitions and their interrelations is of fundamental importance. While it is widely perceived that their dynamics arises from nontrivial topological configurations in Yang-Mills theories, a concrete and sophisticated realization of such idea is an outstanding challenge. We report significant progress along this direction by the construction of a new framework based on correlated ensemble of instanton-dyons, namely the constituents of the finite-temperature instantons with non-trivial holonomy. We present a comprehensive numerical study of confinement properties in SU(2) Yang-Mills theory at finite temperature, obtaining important observables such as the effective holonomy potential, the static quark potentials from Polyakov loop correlators as well as spatial Wilson loops, among others.

Yield ratios of identified hadrons in p+p, p+Pb , and Pb+Pb collisions at energies available at the CERN Large Hadron Collider

Yield ratios of identified hadrons observed in high multiplicity p+p and p+Pb collisions at LHC show remarkable similarity with those in Pb+Pb collisions, indicating some important and universal underlying dynamics in hadron production for different quark gluon final states. We use the quark combination model to explain the data of yield ratios in these three collision systems. The observed $p/\pi$ and $\Lambda/K_s^0$ can be reproduced simultaneously by quark combination, and these two ratios reflect the rate of baryon production at hadronization which is the same in light sector and strange sector and is roughly constant in p+p, p+Pb and Pb+Pb collision systems over three orders of magnitude in charged particle multiplicity.The data of $K_s^0/\pi$, $\Lambda/\pi$, $\Xi/\pi$ and $\Omega/\pi$ show a hierarchy behavior relating to the strangeness content, and are naturally explained by quark combination both in the saturate stage at high multiplicity and in the increase stage at moderate multiplicity. Our results suggest that the dynamical characteristic of quark combination is necessary in describing the production of hadrons in small systems created in p+p and p+Pb collisions.

Towers of positive parity excited baryons and their mixing in the large Nc limit

We consider configuration mixing for the nonstrange positive parity excited baryons in the $[\mathbf{56'},0^+],[\mathbf{56},2^+], [\mathbf{70},0^+] $ and $[\mathbf{70},2^+]$ quark model $SU(6) \times O(3)$ multiplets contained in the $N=2$ band. Starting from the effective mass operator for these states we show by an explicit calculation that in the large $N_c$ limit they fall into six towers of degenerate states labeled by $K=0,1,1',2,2',3$. We find that the mixing of the quark model states is much simpler than what is naively expected. To leading order in $N_c$ only states carrying the same $K$ label can mix, which implies that for the spin-flavor states we started with configuration mixing can be parameterized by just two constants, $\mu_{K=1}$ and $\mu_{K=2}$.

Quark Wigner distributions using light-front wave functions

The quasiprobabilistic Wigner distributions are the quantum mechanical analog of the classical phase-space distributions. We investigate quark Wigner distributions for a quark state dressed with a gluon, which can be thought of as a simple composite and relativistic spin-$1/2$ state with a gluonic degree of freedom. We calculate various polarization configurations, namely, unpolarized, longitudinally polarized, and transversely polarized quark, and the target state using light-front wave functions in this model. At the leading twist, one can define 16 quark Wigner distributions; however, we obtain only 8 independent nonzero Wigner distributions in our model. We compare our results with other model calculations for the proton.

Intrinsic light and strange quark-antiquark pairs in the proton and nonperturbative strangeness suppression

The CLAS Collaboration recently reported measured ratios of pion and kaon electroproduction cross sections from a proton target and extracted the ratios for light and strange quark--antiquark pairs, ${u\bar{u}}/ {d\bar{d}}$ and ${s\bar{s}}/ {d\bar{d}}$. Within an extended chiral constituent quark formalism, we investigate contributions to those ratios from the nonperturbative mechanism due to all possible intrinsic $|uudQ \bar{Q}\rangle$ Fock states in the proton; with $Q \bar{Q} \equiv u\bar{u},~ d\bar{d},~s\bar{s},~c\bar{c}$. Our results are compared with the CLAS data and findings from other phenomenological approaches, offering insights into the manifestations of the genuine five--quark Fock states in the proton and its relevance to interpreting the experimental data.

Confinement at Finite Temperature

We show the flux tubes produced by static quark–antiquark, quark–quark and quark–gluon charges at finite temperature. The sources are placed on the lattice with fundamental and adjoint Polyakov loops. We compute the squared strengths of the chromomagnetic and chromoelectric fields above and below the critical temperature. Our results are for pure gauge SU(3) gauge theory, they are invariant and all computations are done with GPUs using CUDA.

Magnetic moment of the XQ state with JPC=1+± in light cone QCD sum rules

The magnetic moments of the recently observed resonance $X_b(5568)$ by DO Collaboration and its partner with charm quark are calculated in the framework of the light cone QCD sum rules, by assuming that these resonances are represented as tetra--quark states with quantum numbers $J^{PC}=1^{+\pm}$. The magnetic moment can play critical role in determination of the quantum numbers, as well as giving useful information about the inner structure of these mesons.

Dark matter properties implied by gamma ray interstellar emission models

We infer dark matter properties from gamma ray residuals extracted using eight different interstellar emission scenarios proposed by the Fermi-LAT Collaboration to explain the Galactic Center gamma ray excess. Adopting the most plausible simplified ansatz, we assume that the dark matter particle is a Majorana fermion interacting with standard fermions via a scalar mediator. To trivially respect flavor constraints, we only couple the mediator to third generation fermions. Using this theoretical hypothesis, and the Fermi residuals, we calculate Bayesian evidences, including Fermi-LAT exclusion limits from 15 dwarf spheroidal galaxies as well. Our evidence ratios single out one of the Fermi scenarios as most compatible with the simplified dark matter model. In this scenario the dark matter (mediator) mass is in the 25-200 (1-1000) GeV range and its annihilation is dominated by bottom quark final state. Our conclusion is that the properties of dark matter extracted from gamma ray data are highly sensitive to the modeling of the interstellar emission.

Analysis of nucleon electromagnetic form factors from light-front holographic QCD: The spacelike region

We present a comprehensive analysis of the spacelike nucleon electromagnetic form factors and their flavor decomposition within the framework of light-front holographic QCD. We show that the inclusion of the higher Fock components $\ket {qqqq\bar{q}}$ has a significant effect on the spin-flip elastic Pauli form factor and almost zero effect on the spin-conserving Dirac form factor. We present light-front holographic QCD results for the proton and neutron form factors at any momentum transfer range, including asymptotic predictions, and show that our results agree with the available experimental data with high accuracy. In order to correctly describe the Pauli form factor we need an admixture of a five quark state of about 30$\%$ in the proton and about 40$\%$ in the neutron. We also extract the nucleon charge and magnetic radii and perform a flavor decomposition of the nucleon electromagnetic form factors. The free parameters needed to describe the experimental nucleon form factors are very few: two parameters for the probabilities of higher Fock states for the spin-flip form factor and a phenomenological parameter $r$, required to account for possible SU(6) spin-flavor symmetry breaking effects in the neutron, whereas the Pauli form factors are normalized to the experimental values of the anomalous magnetic moments. The covariant spin structure for the Dirac and Pauli nucleon form factors prescribed by AdS$_5$ semiclassical gravity incorporates the correct twist scaling behavior from hard scattering and also leads to vector dominance at low energy.

Confinement inF4Exceptional Gauge Group Using Domain Structures

We calculate the potential between static quarks in the fundamental representation of the F 4 exceptional gauge group using domain structures of the thick center vortex model. As non-trivial center elements are absent, the asymptotic string tension is lost while an intermediate linear potential is observed. SU (2) is a subgroup of F 4 . Investigating the decomposition of the 26 dimensional representation of F 4 to the SU (2) representations, might explain what accounts for the intermediate linear potential, in the exceptional groups with no center element.

The fermi coupling, mass spectrum and decay properties of mesons within the covariant confined quark model

Main properties of stable quark-antiquark bound states have been investigated by using a relativistic quark model with analytic confinement. A new insight into the problem of hadron mass generation is provided. It has been shown that the compositeness condition expressing the Yukawa coupling of the meson-quark interaction and the master equation relating the meson mass function to the Fermi coupling can together guarantee the equivalency of the both theories, thereby providing an interpretation of the meson field as a bound state of constituent quarks. A smooth behavior for the Fermi coupling G(M) obeying reasonable accuracy for the meson estimated masses M has been obtained. We have also updated our previous numerical results for the weak-decay constants as well as the electromagnetic decay widths of mesons. The obtained estimates are found in reasonable agreement with the recent experimental data.

Measurements of [formula omitted] using the ATLAS detector

The large centre-of-mass energy available at the LHC proton-proton collider allows for copious production of top-quark pairs in association with other final state particles at high transverse momentum. Results on the top-quark pair production in association with W and Z bosons at both 8 and 13 TeV are presented as well as the measurement of the cross section for production with an associated isolated photon at 7 TeV. The ATLAS experiment has measured several final state observables that are sensitive to additional radiation in top anti-top quark final states. Analyses probing the top-quark pair production with additional QCD radiation include the multiplicity of jets for various transverse momentum thresholds in the 13 TeV data. These measurements are compared to some of the most recent Monte Carlo event generators based on NLO QCD or LO multi-leg matrix element calculations.

Instantaneous Bethe–Salpeter view of Goldstone-type pseudoscalar mesons

Describing the lightest pseudoscalar mesons as bound states of quark and antiquark within the framework of an instantaneous Bethe–Salpeter formalism constructed such as to retain (in contrast to Salpeter’s equation) as much information on the relativistic effects provided by the full quark propagator as conceivable allows for a surprisingly simple implementation of their near masslessness mandatory for their interpretability as pseudo-Goldstone bosons related to the spontaneous breaking of the chiral symmetries of quantum chromodynamics.

Constraints on the dark matter annihilation from Fermi-LAT observation of M31

Gamma-ray is a good probe of dark matter (DM) particles in the Universe. We search for the DM annihilation signals in the direction of the Andromeda galaxy (M31) using 7.5 year Fermi-LAT pass 8 data. Similar to Pshirkov et al. (2016), we find that there is residual excess emission from the direction of M31 if only the galactic disk as traced by the far infrared emission is considered. Adding a point-like source will improve the fitting effectively, although additional slight improvements can be found if an extended component such as a uniform disk or two bubbles is added instead. Taking the far infrared disk plus a point source as the background model, we search for the DM annihilation signals in the data. We find that there is strong degeneracy between the emission from the galaxy and that from 10s GeV mass DM annihilation in the main halo with quark final state. However, the required DM annihilation cross section is about 10−25–10−24 cm3s−1, orders of magnitude larger than the constraints from observations of dwarf spheroidal galaxies, indicating a non-DM origin of the emission. If DM subhalos are taken into account, the degeneracy is broken. When considering the enhancement from DM subhalos, the constraints on DM model parameters are comparable to (or slightly weaker than) those from the population of dwarf spheroidal galaxies. We also discuss the inverse Compton scattering component from DM annihilation induced electrons/positrons. For the first time we include an energy dependent template of the inverse Compton emission (i.e., a template cube) in the data analysis to take into account the effect of diffusion of charged particles. We find a significant improvement of the constraints in the high mass range of DM particles after considering the inverse Compton emission.

Vnutrishni stany adroniv u relyatyvists'kykh systemakh vidliku

The internal state of a composite particle and its transformation, when changing from the reference frame, where this composite particle is at rest, to a reference frame, where it moves relativistically, have been considered. It is supposed that the internal state of the composite particle in its rest frame can be considered in the non-relativistic approximation. This internal state is shown to remain the same, when changing from one inertial reference frame to another one. In other words, a particle that is spherically symmetric in its rest frame does not change its form in any other reference frame and does not undergo the Lorentz contraction in the direction of motion of any reference frame with respect to the rest one. A possible application of the results obtained to describe the scattering of hadrons considered as bound states of quarks has been discussed.

Thermal width of heavy quarkonia from an AdS/QCD model

We estimate the thermal width of a heavy quark anti-quark pair inside a strongly coupled plasma using a holographic AdS/QCD model. The imaginary part of the quark potential that produces the thermal width appears in the gravity dual from quantum fluctuations of the string world sheet in the vicinity of the horizon. The results, obtained using a soft wall background that involves an infrared mass scale, are consistent with previous analisys where the mass scale was introduced by averaging over quark anti-quark states.

P -wave coupled channel effects in electron-positron annihilation

$P$-wave coupled channel effects arising from the $D\overline{D}$, $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}.$, and ${D}^{*}{\overline{D}}^{*}$ thresholds in ${e}^{+}{e}^{\ensuremath{-}}$ annihilations are systematically studied. We provide an exploratory study by solving the Lippmann-Schwinger equation with short-ranged contact potentials obtained in the heavy quark limit. These contact potentials can be extracted from the $P$-wave interactions in the ${e}^{+}{e}^{\ensuremath{-}}$ annihilations, and then be employed to investigate possible isosinglet $P$-wave hadronic molecules. In particular, such an investigation may provide information about exotic candidates with quantum numbers ${J}^{\mathrm{PC}}={1}^{\ensuremath{-}+}$. In the mass region of the $D\overline{D}$, $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}.$, and ${D}^{*}{\overline{D}}^{*}$ thresholds, there are two quark model bare states, i.e. the $\ensuremath{\psi}(3770)$ and $\ensuremath{\psi}(4040)$, which are assigned as $({1}^{3}{D}_{1})$ and $({3}^{1}{S}_{1})$ states, respectively. By an overall fit of the cross sections of ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}D\overline{D}$, $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}.$, ${D}^{*}{\overline{D}}^{*}$, we determine the physical coupling constants to each channel and extract the pole positions of the $\ensuremath{\psi}(3770)$ and $\ensuremath{\psi}(4040)$. The deviation of the ratios from that in the heavy quark spin symmetry (HQSS) limit reflects the HQSS breaking effect due to the mass splitting between the $D$ and the ${D}^{*}$. Besides the two poles, we also find a pole a few MeV above the $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}.$ threshold which can be related to the so-called $G(3900)$ observed earlier by BABAR and Belle. This scenario can be further scrutinized by measuring the angular distribution in the ${D}^{*}{\overline{D}}^{*}$ channel with high luminosity experiments.

Single quark entropy and the Polyakov loop

We study Quantum Chromodynamics (QCD) with 2 + 1 flavors with almost physical quark masses using the highly improved staggered quark action (HISQ). We calculate the Polyakov loop in a wide temperature range, obtain the free energy and the entropy of a single static quark and discuss the QCD crossover region in detail. We show that the entropy has a peak close to the chiral crossover and consider the consequences for the deconfinement aspects of the crossover phenomena. We study the renormalized Polyakov loop susceptibilities and place them into the context of the crossover. We also obtain a quantitative result for the onset of weak-coupling behavior at high temperatures.

Remarks on meson loop effects on quark models

We investigate the effect of meson loops on the spectrum of quark states. We demonstrate that in general quark states do not tend to get very broad if their coupling to the continuum increases, but instead they decouple from the latter in the large coupling limit. We ascribe this effect to the essentially nonperturbative unitarization procedure involved. In the meantime, some quark resonances behave very differently and demonstrate collectivity in the sense that their pole trajectories span a wide, as compared to the level spacing, region therefore acquiring contributions from multiple bare poles rather than from the closest neighbors. While the actual calculations are done within particular, very simplified models, it is argued that the findings might well be general.

Searches for Heavy Quark States at ATLAS

This talk highlights the latest results of heavy quark searches from the ATLAS collaboration, mainly on resonance searches and vector-like quarks (VLQs) searches. Searches for it resonances using lepton-plus-jets events in proton-proton collisions at center-of-mass energy of 8 and 13 TeV are presented. Limits are set for BSM particles such as topcolor-assisted technicolor Z'TC, Kaluza-Klein (K-K) gluons gKK and K-K excitations of graviton GKK in the Randall-Sundrum model of extra dimensions. VLQs arise naturally in many models such as Little Higgs and Composite Higgs and typically couple preferably to the third generation SM quarks and weak bosons. Limits are set for vector-like bottom (B) and top (T) quarks decay to lepton-plus-jets final states via Hb+X and Ht+X channels in two analyses using 8 and 13 TeV datasets from ATLAS.