Quark Systems Research Articles

Global tensor polarization of spin 3/2 hadrons and quark spin correlations in relativistic heavy ion collisions

We study the global polarization of spin-3/2 hadrons in relativistic heavy ion collisions. We show in particular that the global tensor polarizations of rank two or three for spin-3/2 hadrons are sensitive to the local two or three quark spin correlations respectively in the quark gluon plasma produced in the collision processes. We present the relationships between these measurable tensor polarizations and quark spin correlations in the quark matter system. Published by the American Physical Society 2024

Gluon generalized TMDs and Wigner distributions in boost invariant longitudinal space

We present the gluon generalized TMDs for non-zero skewness and Wigner distributions in the boost invariant longitudinal space. The boost-invariant longitudinal space is defined as σ=12b−Δ+ and is conjugate to the skewness variable ξ. We use the dressed quark model, where a high-energetic quark is dressed by a gluon. This two-particle system has the advantage of addressing both the gluon and the quark sectors. The different contributions in Wigner distributions coming from different polarization of gluon and the dressed quark system are investigated.

The dense QCD equation of state within a modified NJL model

In this paper, we study the 2-flavor equation of state of the quantum chromodynamics at zero temperature and finite chemical potentials with a modified Nambu–Jona–Lasinio model, where the beta equilibrium and electric charge neutrality conditions of the system (including u, d quarks, electrons and muons) are considered. The related chiral phase transition is also discussed in this paper. For comparison, we show the results with four different parameter sets, and find only quantitative differences. As chemical potential increases, the crossover instead of first-order chiral phase transition happens. Finally, we calculate the binding energy per baryon for different parameter sets, and find that the 2-flavor quark system with a smaller [Formula: see text] (or a larger m) possesses the lower binding energy per baryon, indicated to be more stable than the other case.

The Parallel Compact Object CALculator: An Efficient General Relativistic Initial Data Solver for Compact Objects

Every numerical general relativistic investigation starts from the solution of the initial value equations at a given time. Astrophysically relevant initial values for different systems lead to distinct sets of equations that obey specific assumptions tied to the particular problem. Therefore, a robust and efficient solver for a variety of strongly gravitating sources is needed. In this work, we present the OpenMP version of the Compact Object CALculator (COCAL) on shared memory processors. We performed extensive profiling of the core COCAL modules in order to identify bottlenecks in efficiency, which we addressed. Using modest resources, the new parallel code achieves speedups of approximately one order of magnitude relative to the original serial COCAL code, which is crucial for parameter studies of computationally expensive systems such as magnetized neutron stars, as well as its further development towards more realistic scenarios. As a novel example of our new code, we compute a binary quark system where each companion has a dimensionless spin of 0.43 aligned with the orbital angular momentum.

Dibaryons and where to find them

In recent years, there has been tremendous progress in the investigation of bound systems of quarks with multiplicities beyond the more usual two- and three-quark systems. Experimental and theoretical progress has been made in the four-, five- and even six-quark sectors. In this paper, we review the possible lightest six-quark states using a simple ansatz based on SU(3) symmetry and evaluate the most promising decay branches. The work will be useful to help focus future experimental searches in this six-quark sector.

Quantum Chromodynamics of the Nucleon in Terms of Complex Probabilistic Processes

Despite the obvious progress made by the Feynman, Ravndal, and Kislinger relativistic model in describing the internal motion of a system with confinement of quarks in a nucleon, it turned out to be insufficiently realistic for a number of reasons. In particular, the model does not take into account some cornerstone properties of QCD, namely, gluon exchange between quarks, the influence of the resulting quark sea on valence quarks, and the self-interaction of colored gluons. It is these phenomena that spontaneously break the chiral symmetry of the quark system and form the bulk of the nucleon. To eliminate the above shortcomings of the model, the problem of self-organization of a three-quark dynamical system immersed in a colored quark–antiquark sea is considered within the framework of complex probabilistic processes that satisfy the stochastic differential equation of the Langevin–Kline–Gordon–Fock type. Taking into account the hidden symmetry of the internal motion of a dynamical system, a mathematically closed nonperturbative approach was developed, which makes it possible to construct the mathematical expectation of the wave function and other parameters of the nucleon in the form of multiple integral representations. It is shown that additional subspaces arising in a representation characterized by a noncommutative geometry with topological features participate in the formation of an effective interaction between valence quarks against the background of harmonic interaction between them.

Exploring the Power of Graph Theory in Hadron Theory: From Bound States to Quark Systems

<p>The article discusses how graph theory has been utilized in hadron theory for high energy interactions in recent years. The paper emphasizes the significance of a visual perspective throughout the discussion and explores how graph theory can aid in creating various systems such as bound state systems. Additionally, the paper delves into how graph theory has been used to develop few-body quark systems and how it can connect with adjacency and incidence matrices in the graph theory by providing examples of how these fundamental principles have been applied to topics ranging from hadronic bound states.</p>

Systematic analysis of doubly charmed baryons $$\Xi _{cc}$$ and $$\Omega _{cc}$$

In this work, we perform a systematic study of the mass spectra, the root mean square(r.m.s.) radii and the radial density distributions of the doubly charmed baryons $\Xi_{cc}$ and $\Omega_{cc}$. The calculations are carried out in the frame work of Godfrey-Isgur (GI) relativized quark model, where the baryon is regarded as a real three-body system of quarks. Our results show that the excited energy of doubly charmed baryon with $\rho$-mode is lower than those of the $\lambda$-mode and $\lambda$-$\rho$ mixing mode, which indicates that the lowest state is dominated by the $\rho$-mode. According to this conclusion, we systematically investigate the mass spectra, the r.m.s. radii of the ground and excited states($1S\sim4S$, $1P\sim4P$, $1D\sim4D$, $1F\sim4F$ and $1G\sim4G$) with $\rho$-mode. Using the wave functions obtained from quark model, we also study the radial density distributions. Finally, with the predicated mass spectra, the Regge trajectories of $\Xi_{cc}$ and $\Omega_{cc}$ in the ($J$,$M^{2}$) plane are constructed, and the slopes, intercepts are determined by linear fitting. It is found that model predicted masses fit nicely to the constructed Regge trajectories.

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.

Systematic analysis of single heavy baryons ΛQ, ΣQ and ΩQ

Motivated by great progresses in experiments in searching for the heavy baryons, we systematically analyze the mass spectra and root mean square radius of single heavy baryons ΛQ, ΣQ and ΩQ. The calculations of the mass spectra are carried out in the frame work of relativized quark model, where the baryon is regarded as a three-body system of quarks. Our results show that the mass of single heavy baryon with λ-mode is lower than those of the ρ-mode and λ-ρ mixing mode, which indicates that the lowest state is dominated by the λ-mode. Basing on this research, we systematically calculate the mass spectra and the root mean square radius of the baryons with λ excited mode. With these predicated mass spectra, the Regge trajectories in the (J, M2) plane are constructed, and the slopes, intercepts of the Regge trajectories are obtained by linear fitting. It is found that all available experimental data are well reproduced by model predictions and fit nicely to the constructed Regge trajectories.

Particles Composition and Interactions Using the Nuon Model

The Standard Model in Particle Physics has been able to make many predictions confirmed later with a flow of experimental results. With the discovery of the Higgs boson at the LHC, one is full of admiration for the people contributing to this model fifty years ago and its predictions that have been confirmed gradually. The original particle quark constituent model has evolved with the deep inelastic experiments to a quark and gluons system, then to a more general system with virtual quarks. This work is the result of observations while working at CERN in Geneva with many different experiments at the ISR, SPS, LEP, LHC colliders. A new model based on nuons is introduced, that allows accurate evaluations of the particle masses (mesons and baryons) and magnetic moment, computes very accurately the kinematics distributions for particles and jets observed in the p-p collisions at the LHC (elastic and inelastic) and at lower energy machines. This new model looks at a first glance in contradiction with the quark model because it can build the elementary particles with nuons only, i.e. electrons and neutrinos. However, all the existing physics involved in electron, positron and neutrino interactions may be used to explain interactions between composite particles such as protons or heavy ions.

Spin-orbital coupling in strong interaction and global spin polarization

In non-central relativistic heavy ion collisions, the colliding nuclear system possesses a huge global orbital angular momentum in the direction opposite to the normal of the reaction plane. Due to the spin-orbit coupling in strong interaction, such a huge orbital angular momentum leads to a global spin polarization of the quark matter system produced in the collision process. The global polarization effect in high energy heavy ion collisions was first predicted theoretically and confirmed by STAR experiments at the Relativistic Heavy Ion Collider in Brookhaven National Laboratory. The discovery has attracted much attention to the study of spin effects in heavy ion collision and leads to a new direction in high energy heavy ion physics—Spin Physics in Heavy Ion Collisions. In this paper, we briefly review the original ideas, the calculation methods, the main results and recent theoretical developments in last years. First, we present a short discussion of the spin-orbit coupling which is an intrinsic property for a relativistic fermionic quantum system. Then we review how the global orbital angular momentum can be generated in non-central heavy ion collisions and how the global orbital angular momentum can be transferred to the local orbital angular momentum distribution in two limit model---Landan fireball model and Bjorken scaling model. After that, we review how we can describe the scattering process with initial local orbital angular momentum in the formalism of scattering cross section in impact parameter space and how we calculate the polarization of the quarks and antiquarks in quark gluon plasma produced in non-central heavy ion collisions after single or multiple scattering. We also give a brief review on how the global polarization can be predicted from the formalism of relativistic hydrodynamics with the generalized Cooper-Frye formula with spin. Finally, we discuss how the quark's polarization can be transferred to the final hadron's polarization. We focus on the hyperon's polarization and vector meson's spin alignment produced in heavy-ion collisions.

Toward a stringy description for the QQ¯qq¯ -quark system

For the case of two light flavors we propose the stringy description of the system made of one heavy and one light quark-antiquark pair, with the aim of exploring the two lower-lying Born-Oppenheimer potentials as a function of a separation of the heavy quark-antiquark pair. Our analysis reveals three critical separations related to the processes of string reconnection, breaking and junction annihilation. In particular, for the ground state potential only the process of string reconnection matters. We find that a tetraquark state makes the dominant contribution to the potential of the first excited state at small separations, and this is the big difference with the $QQ\bar q\bar q$-quark system where it does so to the ground state potential. Another big difference is the emergence of the full diquark picture $[Qq][\bar Q\bar q]$ rather than the partial picture $QQ[\bar q\bar q]$ for the tetraquark state. On the other hand, the scales of string junction annihilation, below which the systems can be thought of mainly as the compact tetraquarks, are very close for both cases and become almost the same if the phenomenological rule $E_{QQ}=\frac{1}{2} E_{Q\bar Q}$ holds. The same is also true for the screening lengths whose values are in agreement with lattice QCD.

Effects of a Finite Volume in the Phase Structure of QCD

Working in the SU(2) flavor version of the NJL model, we study the effect of taking a finite system volume on a strongly interacting system of quarks, and, in particular, the location of the chiral phase transition and the CEP. We consider two shapes for the volume, spherical and cubic regions with different sizes and different boundary conditions. To analyze the QCD phase diagram, we use a novel criterion to study the crossover zone. A comparison between the results obtained from the two different shapes and several boundary conditions is carried out. We use the method of Multiple Reflection Expansion to determine the density of states and three kinds of boundary conditions over the cubic shape. These boundary conditions are: periodic, anti-periodic and stationary boundary conditions on the quark fields.

Quantum fluctuation in an inhomogeneous background and its influence on the phase transition in a finite volume system

We have studied the grand potential and phase transitions of an inhomogeneous finite volume spherical quark system. First the finite volume effects are considered by applying the multiple reflection expansion method which is an approximation for the density of states of the momentum in the grand potential of the finite size system. Then, the density of states of momentum is further modified by the thermal fluctuations in the thermal system with the inhomogeneous field background. The modification of the density of states is calculated by the scattering phase shift from the Dirac equation of quarks in the inhomogeneous field background. By the numerical calculation we show how the phase transition is changed by varying the configuration of the inhomogeneous field background and find that the strong first order phase transition could be weakened or even changed to a crossover as a result.

Spectrum of SU(2) gauge theory at large number of flavors

We present a numerical study of the spectrum of an asymptotically nonfree SU(2) gauge theory with ${N}_{f}=24$ massive fermion flavors. For such a large number of flavors, asymptotic freedom is lost and the massless theory is governed by a Gaussian fixed point at long distances. If fermions are massive they decouple at low energy scales and the theory is confining. We present a scaling law for the masses of the hadrons, glueballs and string tension as functions of fermion mass. The hadrons become effectively heavy quark systems, with masses approximately twice the fermion mass, whereas the energy scale of the confinement, probed by e.g., the string tension, is much smaller and vanishes asymptotically as ${m}_{\text{fermion}}^{2.18}$. Our results from lattice simulations are compatible with this behavior.

PNJL model at zero temperature: The three-flavor case

We propose a three-flavor version of the Polyakov-Nambu-Jona-Lasino (PNJL) model at zero temperature regime, by implementing a traced Polyakov loop ($\Phi$) dependence in the scalar, vector and 't Hooft channel strengths. We study the thermodynamics of this model, named as PNJL0, with special attention for the first order confinement/deconfinement phase transition for which $\Phi$ is the order parameter. For the symmetric quark matter case, an interesting feature observed is a strong reduction of the constituent strange quark mass ($M_s$) at the chemical potential related to point where deconfinement takes place. The emergence of $\Phi$ favors the restoration of chiral symmetry even for the strange quark. We also investigate the charge neutral system of quarks and leptons in weak equilibrium. As an application, we construct a hadron-quark phase transition with a density dependent hadronic model coupled to the SU(3) PNJL0 model. In this case, the quark side is composed by deconfined particles. This approach is used to determine mass-radius profiles compatible with recent data from the Neutron Star Interior Composition Explorer (NICER) mission.

Gluons, light and heavy quarks in the instanton vacuum

In this paper, we put our focus towards describing the nonperturbative effects in the properties of hadrons made from the light-heavy and the heavy–heavy quarks in the framework of Instanton Liquid Model (ILM) of QCD vacuum. The main features of ILM and its applicability in the heavy quark sector are briefly discussed. The properties of gluonic systems, the light and heavy quark correlators in the instanton background are also analyzed. We demonstrate that the consideration of both, perturbative and nonperturbative, gluon effects in the instanton background for a single heavy quark leads to the mass shift due to the direct-instanton nonperturbative and ILM modified perturbative contributions, respectively. For the interacting heavy quark and heavy anti-quark, the potential consists of the direct instanton-induced part and the one-gluon exchange (OGE) perturbative part. OGE interactions are screened at large distances due to the nonperturbative dynamics. The estimation of instanton contributions in the phenomenological Cornell-type potential model is presented. In relation to the experimental data, the charmonium properties, the role of instanton effects in their spectra and transitions are discussed. The main features of heavy-light quark systems in the instanton generated background are also discussed. As an example, we consider the process of pion emissions by the exited heavy quarkonium. We show that there is a sizable correction ([Formula: see text]) to the dipole approximation for the process [Formula: see text].

Structure of the X(3872) as explained by a diffusion Monte Carlo calculation

Two decades after its unexpected discovery, the properties of the $X(3872)$ exotic resonance are still under intense scrutiny. In particular, there are doubts about its nature as an ensemble of mesons or having any other internal structure. We use a Diffusion Monte Carlo method to solve the many-body Schr\"odinger equation that describes this state as a $c \bar c n \bar n$ ($n=u$ or $d$ quark) system. This approach accounts for multi-particle correlations in physical observables avoiding the usual quark-clustering assumed in other theoretical techniques. The most general and accepted pairwise Coulomb$\,+\,$linear-confining$\,+\,$hyperfine spin-spin interaction, with parameters obtained by a simultaneous fit of around 100 masses of mesons and baryons, is used. The $X(3872)$ contains light quarks whose masses are given by the mechanism responsible of the dynamical breaking of chiral symmetry. The same mechanisms gives rise to Goldstone-boson exchange interactions between quarks that have been fixed in the last 10-20 years reproducing hadron, hadron-hadron and multiquark phenomenology. It appears that a meson-meson molecular configuration is preferred but, contrary to the usual assumption of $D^0\bar{D}^{\ast0}$ molecule for the $X(3872)$, our formalism produces $\omega J/\psi$ and $\rho J/\psi$ clusters as the most stable ones, which could explain in a natural way all the observed features of the $X(3872)$.

Remarks on static three-quark potentials, string breaking and gauge/string duality

Making use of the gauge/string duality, it is possible to study some aspects of the string breaking phenomenon in the three quark system. Our results point out that the string breaking distance is not universal and depends on quark geometry. The estimates of the ratio of the string breaking distance in the three quark system to that in the quark-antiquark system would range approximately from $\frac{2}{3}$ to $1$. In addition, it is shown that there are special geometries which allow more than one breaking distance.