Antiquark System Research Articles

Theoretical Perspectives on Viscous Nature of Strongly Interacting Systems

Matter prevailing during the early stages of the Universe or under extreme conditions in high-energy heavy-ion experiments supposedly possesses a rich phase structure. During the evolution of such a system, the complicated pictures of transitions among various phases are studied as part of hydrodynamics. This system, on most occasions, is considered to be non-viscous. However, various theoretical studies reveal the importance of incorporating viscous effects into the analysis. Here, the paper discusses the behavioral patterns of transport coefficients with varying temperatures and chemical potentials to obtain a qualitative, if not quantitative, picture of the same. Discussions are also shared regarding their impacts on such an exotic system for different energies, as explored in the experimental domain. This theoretical analysis, made using the structure of the Polyakov–Nambu–Jona-Lasinio (PNJL) model with a 2+1-flavor quark–antiquark system reveals important aspects of the inclusion of viscous effects in the hydrodynamic studies of QGP.

Quantum computing for heavy quarkonium spectroscopy

We report a first demonstration for the application of quantum computing to heavy quarkonium spectroscopy study. Based on a Cornell-potential model for the heavy quark and antiquark system, we show how this Hamiltonian problem can be formulated and solved with the VQE approach on the IBM cloud quantum computing platform. Errors due to a global depolarizing noise channel are corrected with a zero-noise extrapolation method, resulting in good agreement with the expected value. We also extend the calculation to excited states on a noiseless quantum simulator by orthogonalization with respect to the ground state.

Statistical method in quark combination model * * Supported by National Natural Science Foundation of China (11535012, 11890713, 11575100), the 973 program (2015CB856902), the Key Research Program of the Chinese Academy of Sciences (XDPB09), and Shandong Province Natural Science Foundation (ZR2019YQ06, ZR2019MA053)

We present a new method for solving the probability distribution for baryons, antibaryons, and mesons at the hadronization of the constituent quark and antiquark system. The hadronization is governed by the quark combination rule in the quark combination model developed by the Shandong Group. We employ the method of the generating function to derive the outcome of the quark combination rule, which is significantly simpler and easier to generalize than the original method. Furthermore, we use the formula of the quark combination rule and its generalization to study the property of the multiplicity distribution of net-protons. Taking a naive case of quark number fluctuations and correlations at hadronization, we calculate ratios of multiplicity cumulants of final-state net-protons and discuss the potential applicability of the quark combination model by studying hadronic multiplicity fluctuations and the underlying phase transition property in relativistic heavy-ion collisions.

A study of stress-tensor distribution around the flux tube in the Abelian–Higgs model

Abstract We study the stress-tensor distribution around the flux tube in static-quark and anti-quark systems based on the momentum conservation and the Abelian–Higgs (AH) model. We first investigate constraints on the stress-tensor distribution from the momentum conservation and show that the effect of boundaries plays a crucial role in describing the structure of the flux tube in SU(3) Yang–Mills theory, which has recently been measured on the lattice [R. Yanagihara, T. Iritani, M. Kitazawa, M. Asakawa, and T. Hatsuda, Phys. Lett. B 789, 210 (2019)]. We then study the distributions of the stress tensor and energy density around the magnetic vortex with and without boundaries in the AH model, and compare them with the distributions in SU(3) Yang–Mills theory based on the dual superconductor picture. It is shown that a wide parameter range of the AH model is excluded by a comparison with the lattice results in terms of the stress tensor.

Correction to the energy spectrum of S10 heavy quarkonia due to two-gluon annihilation effect

In this work, the non-relativistic asymptotic behavior of the transition $q\overline{q}\rightarrow2g\rightarrow q\overline{q}$ in the $^1S_0$ channel is discussed. Different with the usual calculation which expands the physical amplitude around the quark anti-quark threshold, we take the quark anti-quark pairs as off shell and only expand the expression on the three-dimensional momenta of the quarks and anti-quarks. We calculate the results to order 6. The imagine part of the results after applying the on shell conditions can reproduce the non-relativistic QCD (NRQCD) results in leading order of $\alpha_s$. The real part of the results can be used to estimate the mass shift of the $^1S_0$ heavy quark anti-quark system due to the $2g$ annihilation effect. The results can also be used to estimate the energy shifts of the positronium system due to the two-photon annihilation.

Search for dark matter produced in association with a Higgs boson decaying to a pair of bottom quarks in proton\u2013proton collisions at sqrt{s}=13,text {Te}text {V}

A search for dark matter produced in association with a Higgs boson decaying to a pair of bottom quarks is performed in proton–proton collisions at a center-of-mass energy of 13,text {Te}text {V} collected with the CMS detector at the LHC. The analyzed data sample corresponds to an integrated luminosity of 35.9,text {fb}^{-1}. The signal is characterized by a large missing transverse momentum recoiling against a bottom quark–antiquark system that has a large Lorentz boost. The number of events observed in the data is consistent with the standard model background prediction. Results are interpreted in terms of limits both on parameters of the type-2 two-Higgs doublet model extended by an additional light pseudoscalar boson mathrm {a} (2HDM+mathrm {a}) and on parameters of a baryonic mathrm {Z}' simplified model. The 2HDM+mathrm {a} model is tested experimentally for the first time. For the baryonic mathrm {Z}' model, the presented results constitute the most stringent constraints to date.

Spectra of heavy\u2013light mesons in a relativistic model

The spectra and wave functions of heavy–light mesons are calculated within a relativistic quark model which is based on a heavy-quark expansion of the instantaneous Bethe–Salpeter equation by applying the Foldy–Wouthuysen transformation. The kernel we choose is the standard combination of linear scalar and Coulombic vector. The effective Hamiltonian for heavy–light quark–antiquark system is calculated up to order 1/m_Q^2. Our results are in good agreement with available experimental data except for the anomalous D_{s0}^*(2317) and D_{s1}(2460) states. The newly observed heavy–light meson states can be accommodated successfully in the relativistic quark model with their assignments presented. The D_{sJ}^*(2860) can be interpreted as the |1^{3/2}D_1rangle and |1^{5/2}D_3rangle states being members of the 1D family with J^P=1^- and 3^-.

Measurement of the forward-backward asymmetry in top quark-antiquark production inpp¯collisions using thelepton+jetschannel

We present a measurement of the forward–backward asymmetry in top quark–antiquark production using the full Tevatron Run II data set collected by the D0 experiment at Fermilab. The measurement is performed in lepton+jets final states using a new kinematic fitting algorithm for events with four or more jets and a new partial reconstruction algorithm for events with only three jets. Corrected for detector acceptance and resolution effects, the asymmetry is evaluated to be AFB=(10.6±3.0)%. Results are consistent with the standard model predictions which range from 5.0% to 8.8%. We also present the dependence of the asymmetry on the invariant mass of the top quark–antiquark system and the difference in rapidities of the top quark and antiquark.3 MoreReceived 23 May 2014DOI:https://doi.org/10.1103/PhysRevD.90.072011© 2014 American Physical Society

A confining quark model and new gauge symmetry

We discuss a confining model for quark–antiquark system with a new color SU3 gauge symmetry. New gauge transformations involve non-integrable phase factors and lead to the fourth-order gauge field equations and a linear potential. The massless gauge bosons have non-definite energies, which are not observable because they are permanently confined in quark systems by the linear potential. We use the empirical potentials of charmonium to determine the coupling strength of the color charge gs and find [Formula: see text]. The rules for Feynman diagrams involve propagators with poles of order 2 associated with new gauge fields. The confining quark model may be renormalizable by power counting and compatible with perturbation theory.

Measurements of tt spin correlations and top-quark polarization using dilepton final states in pp collisions at sqrt[s]=7 TeV.

Spin correlations and polarization in the top quark-antiquark system are measured using dilepton final states produced in pp collisions at the LHC at sqrt[s]=7 TeV. The data correspond to an integrated luminosity of 5.0 fb(-1) collected with the CMS detector. The measurements are performed using events with two oppositely charged leptons (electrons or muons), a significant imbalance in transverse momentum, and two or more jets, where at least one of the jets is identified as originating from a b quark. The spin correlations and polarization are measured through asymmetries in angular distributions of the two selected leptons, unfolded to the parton level. All measurements are found to be in agreement with predictions of the standard model.

Rotating mesons in the presence of higher derivative corrections from gauge–string duality

We consider a rotating quark–antiquark ( q q ¯ ) pair in N = 4 thermal plasma. By using the AdS/CFT correspondence, the properties of this system are investigated. In particular, we study variation of a rotating string radius at the boundary as a function of its tip and angular velocity. We also extend the results to higher derivative corrections, i.e. R 2 and R 4 which correspond to finite coupling corrections on the rotating quark–antiquark system in the hot plasma. In the R 4 case and for fixed angular velocity the string endpoints become more and more separated as λ − 1 decreases. To study R 2 corrections, rotating quark–antiquark system in Gauss–Bonnet background has been considered. We summarize the effects of these corrections in the conclusion section.

Comparison of gluon flux-tube distributions for quark-diquark and quark-antiquark hadrons

The distribution of gluon fields in hadrons is of fundamental interest in QCD. Using lattice QCD we have observed the formation of gluon flux tubes within 3 quark (baryon) and quark plus antiquark (meson) systems for a wide variety of spatial distributions of the color sources. In particular we have investigated three quark configurations where two of the quarks are close together and the third quark is some distance away, which approximates a quark plus diquark string. We find that the string tension of the quark-diquark string is the same as that of the quark-antiquark string on the same lattice. We also compare the longitudinal and transverse profiles of the gluon flux tubes for both sets of strings, and find them to be of similar radii and to have similar vacuum suppression.

A pentaquark model for Λ(1405)

We study a pentaquark model of the negative parity hyperon Lambda(1405). We choose a specific quark configuration for trial, and use the perturbative chiral quark model extended to four quarks and one anti-quark system. We calculate a sigma-term and a scalar form factor of the hyperon and demonstrate their usefulness to study the nature of the hyperon.

Radiative decays of quarkonium states, momentum operator expansion and nilpotent operators

We present the method of calculation of the radiative decays of composite quark–antiquark systems, with different J PC: . The method is relativistic invariant; it is based on the double dispersion relation integrals over the masses of the composite mesons; it can be used for high spin particles and provides us with the gauge invariant transition amplitudes. We apply this method to the case when the photon is emitted by a constituent in the intermediate state (additive quark model). We perform the momentum operator expansion of the spin amplitudes for the decay processes. The problem of the nilpotent spin operators is discussed.

Analytic solution of the Schrödinger equation for the Coulomb-plus-linear potential. I. The wave functions

We solve the Schrödinger equation for a quark–antiquark system interacting via a Coulomb-plus-linear potential, and obtain the wave functions as power series, with their coefficients given in terms of the combinatorics functions.

Mass spectra and leptonic decay widths of heavy quarkonia by using psi function

In this study, a non-relativistic two-body wave equation is used to describe the properties of heavy quark–antiquark systems with a potential proportional to the ψ-function. The wave equation is transformed into a true eigenvalue equation and solved numerically. Both the resonance masses and the leptonic decay widths of and mesons are calculated. The obtained results showed that the quark–antiquark interaction in these systems could be described adequately by using this simple potential form which contains one adjustable parameter besides the quark masses.

Variationally improved perturbation theory and the potential −α/r + βr

Variationally improved perturbation theory is applied to the potential −αr + βr,which is relevant to heavy quark–antiquark systems. The problem is advocated asan instructive ‘laboratory’ for undergraduate exploration.

A VARIATIONAL FOCK-SPACE TREATMENT OF QUARKONIUM

The variational method and the Hamiltonian formalism of QCD are used to derive relativistic, momentum space integral equations for a quark–antiquark system with an arbitrary number of gluons present. As a first step, the resulting infinite chain of coupled equations is solved in the nonrelativistic limit by an approximate decoupling method. Comparison with experiment allows us to fix the quark mass and coupling constant, allowing for the calculation of the spectra of massive systems such as charmonium and bottomonium. Studying the results with and without the non-Abelian terms, we find that the presence of the non-Abelian factors yields better agreement with the experimental spectra.

Non-Abelianαs3/(mqr2)heavy-quark–antiquark potential

We calculate the leading mass-suppressed two-loop contribution, proportional to ${\ensuremath{\alpha}}_{s}^{3}{/(m}_{q}{r}^{2}),$ to the potential of a heavy-quark--antiquark system. This contribution originates in the non-Abelian nature of quantum chromodynamics (QCD) and has no analogue in quantum electrodynamics. For this purpose, we elaborate a technique based on the implementation of the threshold expansion within the effective theory of nonrelativistic QCD. We discuss the phenomenological implications of our result for heavy-quarkonium physics. We also confirm a previous result for the two-loop $\mathcal{O}({\ensuremath{\alpha}}_{s}^{2})$ correction to the static potential.

Charge fluctuations in a quark–antiquark system

It is pointed out that the recent data on charge fluctuations observed in heavy ion collisions are compatible with production of a system of weakly correlated constituent quarks and antiquarks.