Quark Systems Research Articles

Heavy Quarkonia in a Contact Interaction and an Algebraic Model: Mass Spectrum, Decay Constants, Charge Radii and Elastic and Transition Form Factors

For the flavor-singlet heavy quark system of bottomonia, we compute the masses of the ground state mesons in four different channels, namely, pseudo-scalar ($\eta_{b}(1S)$), vector ($\Upsilon(1S)$), scalar ($\chi_{b_0}(1P)$) and axial vector ($\chi_{b_{1}}(1P)$). We also calculate the weak decay constants of the $\eta_{b}(1S)$ and $\Upsilon(1S)$ as well as the charge radius of $\eta_{b}(1S)$. It complements our previous study of the corresponding charmonia systems: $\eta_c(1S)$, $J/\Psi(1S)$, $\chi_{c_0}(1P)$) and ($\chi_{c_{1}}(1P)$). The unified formalism for this analysis is provided by a symmetry-preserving Schwinger-Dyson equations treatment of a vector$\times$vector contact interaction. Whenever a comparison is possible, our results are in fairly good agreement with experimental data and model calculations based upon Schwinger-Dyson and Bethe-Salpeter equations involving sophisticated interaction kernels. Within the same framework, we also report the elastic and transition form factors to two photons for the pseudo-scalar channels $\eta_{c}(1S)$ and $\eta_{b}(1S)$ in addition to the elastic form factors for the vector mesons $J/\Psi$ and $\Upsilon$ for a wide range of photon momentum transfer squared ($Q^2$). For $\eta_{c}(1S)$ and $\eta_{b}(1S)$, we also provide predictions of an algebraic model which correlates remarkably well between the known infrared and ultraviolet limits of these form factors.

Theoretical estimation of Photons flow rate Production in quark gluon interaction at high energies

photons emitted from higher energetic collisions in quark-gluon system have been theoretical studied depending on color quantum theory. A simple model for photons emission at quark-gluon system have been investigated. In this model, we use a quantum consideration which enhances to describing the quark system. The photons current rate are estimation for two system at different fugacity coefficient. We discussion the behavior of photons rate and quark gluon system properties in different photons energies with Boltzmann model. The photons rate depending on anisotropic coefficient : strong constant, photons energy, color number, fugacity parameter, thermal energy and critical energy of system are also discussed.

Covariant kinetic theory for effective fugacity quasiparticle model and first order transport coefficients for hot QCD matter

An effective relativistic kinetic theory has been constructed for an interacting system of quarks, anti-quarks and gluons within a quasi-particle description of hot QCD medium at finite temperature and baryon chemical potential, where the interactions are encoded in the gluon and quark effective fugacities with non-trivial energy dispersions. The local conservations of stress-energy tensor and number current require the introduction of a mean field term in the transport equation which produces non-vanishing contribution to the first order transport coefficients. Such contribution has been observed to be significant for the temperatures which are closer to the QCD transition tem- perature, however, induces negligible contributions beyond a few times the transition temperature. As an implication, impact of the mean field contribution on the the temperature dependence of the shear viscosity, bulk viscosity and thermal conductivity of a hot QCD medium in the presence of binary, elastic collisions among the constituents, has been investigated. Visible effects have been observed for the temperature regime closer to the QCD transition temperature.

Small System Collectivity in Relativistic Hadronic and Nuclear Collisions

The bulk motion of nuclear matter at the ultrahigh temperatures created in heavy ion collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider is well described in terms of nearly inviscid hydrodynamics, thereby establishing this system of quarks and gluons as the most perfect fluid in nature. A revolution in the field is under way, spearheaded by the discovery of similar collective, fluid-like phenomena in much smaller systems including p+ p, p+ A, d+Au, and3He+Au collisions. We review these exciting new observations and their profound implications for hydrodynamic descriptions of small and/or out-of-equilibrium systems.

The meaning behind observed pT regions at the LHC energies

We argue that [Formula: see text] distribution data from the LHC on the invariant differential yield of the charged primary particles in [Formula: see text] collisions at [Formula: see text] and in Pb–Pb collisions at [Formula: see text]TeV with six centrality bins contains several [Formula: see text] regions with special properties. These distributions were analyzed by fitting the data with exponential functions. We conclude that the regions reflect features of fragmentation and hadronization of partons through the string dynamics. The nuclear transparency results in negligible influence of the medium in the III region ([Formula: see text]), which has highest [Formula: see text] values. The effects and changes by the medium start to appear weakly in the II region ([Formula: see text]) and become stronger in the I region ([Formula: see text]). It seems that the II region has highest number of strings. The increase in string density in this region could lead to fusion of strings, appearance of a new string and collective behavior of the partons in the most central collisions. These phenomena can explain anomalous behavior of the Nuclear Modification Factor in the II region. We propose the II region as a possible area of Quark Gluon Plasma formation through string fusion. The first [Formula: see text] regions are the ones with the maximum number of hadrons and minimum number of strings due to direct hadronization of the low energy strings into two quark systems–mesons.

Shedding Light on Hexaquarks

Several new findings in the four, five and six quark systems reheat the interest in the field of multiquark states (beyond the trivial [Formula: see text] and [Formula: see text]). A lot of progress has recently been made in the 6q sector, on both the theoretical and experimental side. A resonance like structure observed in double-pionic fusion to the deuteron, at M = 2.38 GeV with [Formula: see text] = 70 MeV and [Formula: see text] has been consistently observed in a wealth of reaction channels, supporting the existence of a resonant dibaryon state - the [Formula: see text]. These studies include measurement of all the principle strong decay channels in pn collisions in the quasifree mode by the WASA-at-COSY and HADES collaborations. The internal structure of the [Formula: see text] is largely unknown. It can contain various ”hidden color” 6q configurations, [Formula: see text] molecular states with angular momentum L = 0,2,4,6 as well as meson-assisted dressed dibaryon structures. The large set of experimental data obtained to date gives some constraints on the internal structure of the [Formula: see text] dibaryon, but does not settle the issue. The [Formula: see text] is the only multiquark state which can be produced copiously at current facilities, offering unique access to information beyond its basic quantum numbers, particularly its physical size and internal structure.

Critical point in the phase diagram of primordial quark-gluon matter from black hole physics

Strongly interacting matter undergoes a crossover phase transition at high temperatures $T\sim 10^{12}$ K and zero net-baryon density. A fundamental question in the theory of strong interactions, Quantum Chromodynamics (QCD), is whether a hot and dense system of quarks and gluons displays critical phenomena when doped with more quarks than antiquarks, where net-baryon number fluctuations diverge. Recent lattice QCD work indicates that such a critical point can only occur in the baryon dense regime of the theory, which defies a description from first principles calculations. Here we use the holographic gauge/gravity correspondence to map the fluctuations of baryon charge in the dense quark-gluon liquid onto a numerically tractable gravitational problem involving the charge fluctuations of holographic black holes. This approach quantitatively reproduces ab initio results for the lowest order moments of the baryon fluctuations and makes predictions for the higher order baryon susceptibilities and also for the location of the critical point, which is found to be within the reach of heavy ion collision experiments.

Strange Quark Stars in Binaries: Formation Rates, Mergers, and Explosive Phenomena

Abstract Recently, the possible coexistence of a first family composed of “normal” neutron stars (NSs) with a second family of strange quark stars (QSs) has been proposed as a solution of problems related to the maximum mass and to the minimal radius of these compact stellar objects. In this paper, we study the mass distribution of compact objects formed in binary systems and the relative fractions of quark and NSs in different subpopulations. We incorporate the strange QS formation model provided by the two-families scenario, and we perform a large-scale population synthesis study in order to obtain the population characteristics. According to our results, the main channel for strange QS formation in binary systems is accretion from a secondary companion on an NS. Therefore, a rather large number of strange QSs form by accretion in low-mass X-ray binaries and this opens the possibility of having explosive GRB-like phenomena not related to supernovae and not due to the merger of two NSs. The number of double strange QS systems is rather small, with only a tiny fraction that merge within a Hubble time. This drastically limits the flux of strangelets produced by the merger, which turns out to be compatible with all limits stemming from Earth and lunar experiments. Moreover, this value of the flux rules out at least one relevant channel for the transformation of all NSs into strange QSs by strangelets’ absorption.

Magnetic field influence on the early-time dynamics of heavy-ion collisions

In high energy heavy-ion collisions the magnetic field is very strong right after the nuclei penetrate each other and a non-equilibrium system of quarks and gluons builds up. Even though quarks might not be very abundant initially, their dynamics must necessarily be influenced by the Lorentz force. Employing the 3+1d partonic cascade BAMPS we show that the circular Larmor movement of the quarks leads to a strong positive anisotropic flow of quarks at very soft transverse momenta. We explore the regions where the effect is visible, and explicitly show how collisions damp the effect. As a possible application we look at photon production from the flowing non-equilibrium medium.

Quark stars in f(T, mathcal {T})-gravity

We derive a working model for the Tolman–Oppenheimer–Volkoff equation for quark star systems within the modified f(T, mathcal {T})-gravity class of models. We consider f(T, mathcal {T})-gravity for a static spherically symmetric space-time. In this instance the metric is built from a more fundamental tetrad vierbein from which the metric tensor can be derived. We impose a linear f(T) parameter, namely taking f=alpha T(r) + beta mathcal {T}(r) + varphi and investigate the behaviour of a linear energy-momentum tensor trace, mathcal {T}. We also outline the restrictions which modified f(T, mathcal {T})-gravity imposes upon the coupling parameters. Finally we incorporate the MIT bag model in order to derive the mass–radius and mass–central density relations of the quark star within f(T, mathcal {T})-gravity.

Sequential Bottomonium Production at High Temperatures

Bottomonium production in heavy ion collisions is modified compared with any simple extrapolation from elementary collisions. This modification is most likely caused by the presence of a deconfined system of quarks and gluons for times of several fm/c. In such a medium, bottomonium can be destroyed, but the constituent bottom quarks will likely stay spatially correlated due to small mean free paths in this system. With these facts in mind, we describe bottomonium formation with a coupled set of equations. A rate equation describes the destruction of $\Upsilon(1S)$ particles, while a Langevin equation describes how the bottom quarks stay correlated for a sufficiently long time so that recombination into bottomonia is possible. We show that within this approach it is possible to understand the magnitude of $\Upsilon(1S)$ suppression in heavy ion collisions and the larger suppression of the $\Upsilon(2S)$ state, implying that the reduction in the ratio of $\Upsilon(1S)/\Upsilon(2S)$ yield in heavy ion collision does not necessarily correspond to sequential melting picture.

Multiplicity fluctuation and correlation of identified baryons in a quark combination model

The dynamical fluctuation and correlation of multiplicity distributions of identified baryons and antibaryons produced by the hadronization of the bulk quark system are systematically studied in quark combination model. Starting from the most basic dynamics of quark combination which are necessary for multiplicity study, we analyze moments (variance, skewness and kurtosis) of inclusive multiplicity distribution of identified baryons, two-baryon multiplicity correlations, and baryon-antibaryon multiplicity correlations after the hadronization of quark system with given quark number and antiquark number. We obtain a series of interesting findings, e.g., binomial behavior of multiplicity moments, coincide flavor dependent two-baryon correlation and universal baryon-antibaryon correlation, which can be regarded as general features of quark combination. We further take into account correlations and fluctuations of quark numbers before hadronization to study their influence on multiple production of baryons and antibaryons. We find that quark number fluctuation and flavor conservation lead to a series of important results such as the negative $p\bar{\Omega}^{+}$ multiplicity correlation and universal two-baryon correlations. We also study the influence of resonance decay in order to compare our results with future experimental data in ultra-relativistic heavy ion collisions at LHC.

Helium-3 magnetic dipole moment determination by using quark constituents for all possible baryon formations

We perform the calculation of the Helium-3 magnetic dipole moment in quark model of nuclei, by assuming a nucleon’s structure is given in terms of its constituent quark structure. In the Isgur-Karl model framework, we considered nine quark system wave function in ground and first excited states and all possible permutations to calculate the expectation value of the magnetic dipole moment operator of the Helium-3. The result of our calculation is in a better agreement with the experimental value, as compared to shell model and QCD values.

Observable Properties of Quark--Hadron Phase Transition at the Large Hadron Collider

Quark-hadron phase transition is simulated by an event generator that incorporates the dynamical properties of contraction due to QCD confinement forces and randomization due to the thermal behavior of a large quark system on the edge of hadronization. Fluctuations of emitted pions in the $(\eta,\phi)$ space are analyzed using normalized factorial moments in a wide range of bin sizes. The scaling index $\nu$ is found to be very close to the predicted value in the Ginzburg-Landau formalism. The erraticity indices $\mu_q$ are determined in a number of ways that lead to the same consistent values. They are compared to the values from the Ising model, showing significant difference in a transparent plot. Experimental determination of $\nu$ and $\mu_q$ at the LHC are now needed to check the reality of the theoretical study and to provide guidance for improving the model description of quark-hadron phase transition.

Quark confinement, new cosmic expansion and general Yang-Mills symmetry**Supported in part by the Jingshin Resealch Fund of the UMassD Foundation

We discuss a unified model of quark confinement and new cosmic expansion with linear potentials based on a general (SU3)color×(U1)baryon symmetry. The phase functions in the usual gauge transformations are generalized to new ‘action integrals’. The general Yang-Mills transformations have group properties and reduce to usual gauge transformations in special cases. Both quarks and ‘gauge bosons’ are permanently confined by linear potentials. In this unified model of particle-cosmology, physics in the largest cosmos and that in the smallest quark system appear to both be dictated by the general Yang-Mills symmetry and characterized by a universal length. The basic force between two baryons is independent of distance. However, the cosmic repulsive force exerted on a baryonic supernova by a uniform sphere of galaxies is proportional to the distance from the center of the sphere. The new general Yang-Mills field may give a field-theoretic explanation of the accelerated cosmic expansion. The prediction could be tested experimentally by measuring the frequency shifts of supernovae at different distances.

Spectrum of Charmonia within a Contact Interaction

For the flavour-singlet heavy quark system of charmonia, we compute the masses of the ground state mesons in four different channels: pseudo-scalar (ηc(1S)), vector (J/ψ(1S)), scalar (χs0 (1P)) and axial vector (χc1 (1P)), as well as the weak decay constants of the ηc(1S) and J/ψ(1S). The framework for this analysis is provided by a symmetry-preserving Schwinger- Dyson equation (SDEs) treatment of a vector x vector contact interaction (CI). The results found for the meson masses and the weak decay constants, for the spin-spin combinations studied, are in fairly good agreement with experimental data and earlier model calculations based upon Schwinger-Dyson and Bethe-Salpeter equations (BSEs) involving sophisticated interaction kernels.

Spin and pseudo-spin symmetries of fermionic particles with an energy-dependent potential in non-commutative phase space

In this paper, we consider the Dirac equation in two dimensions influenced by an energy-dependent potential within a non-commutative phase space (NCP) framework for which no clear and reasonable solution has been given until now. By using the Nikiforov–Uvarov method to solve our difficult equations we obtain all the allowed energy eigenvalues and wave functions for particles with fermionic statistics, such as heavy quark systems, individual leptons etc. for both pseudo-spin and spin symmetries in the presence and absence of an external magnetic field. Finally we analyze the behavior of the energy values achieved in the NCP space in terms of the system's mass and magnetic field for several n, l levels of the present work.

ηcelastic and transition form factors: Contact interaction and algebraic model

For the flavor-singlet heavy quark system of charmonia in the pseudoscalar ($\eta_c(1S)$) channel, we calculate the elastic (EFF) and transition form factors (TFF) ($\eta_c(1S) \rightarrow \gamma \gamma^*$) for a wide range of photon momentum transfer squared ($Q^2$). The framework for this analysis is provided by a symmetry-preserving Schwinger-Dyson equation (SDE) and Bethe-Salpeter equation (BSE) treatment of a vector$\times$vector contact interaction (CI). We also employ an algebraic model (AM), developed earlier to describe the light quark systems. It correctly correlates infrared and ultraviolet dynamics of quantum chromodynamics (QCD). The CI results agree with the lattice data for low $Q^2$. For $Q^2 \geqslant Q_0^2$, the results start deviating from the lattice results by more than $20 \%$. $Q_0^2 \thickapprox 2.5 {\rm GeV}^2$ for the EFF and $\thickapprox 25 {\rm GeV}^2$ for the TFF. We also present the results for the EFF, TFF as well as $\eta_c(1S)$ parton distribution amplitude for the AM. Wherever the comparison is possible, these results are in excellent agreement with the lattice, perturbative QCD, the results obtained through an SDE-BSE study, employing refined truncations, as well as the experimental findings of the BABAR experiment.

Production and decay of charmed baryons

In this paper, we discuss reactions involving charmed baryons to explore their unique features. A well known phenomenon, the separation of the two internal motions of the ρ and λ types of a three-quark system is revisited. First we discuss the mass spectrum of low lying excitations as function of the heavy quark mass, smoothly connecting the SU(3) and heavy quark limits. The properties of these modes can be tested in the production and decay reactions of the baryons. For production, we consider a one step process which excites dominantly λ modes. We find abundant production rates for some of the excited states. For decay, we study a pion emission process which provides a clean tool to test the structure of heavy quark systems due to the well controlled low energy dynamics of pions and quarks. Both production and decay of charmed baryons are issues for future experiments at J-PARC.

Approximate degeneracy of heavy-light mesons with the same L

Careful observation of the experimental spectra of heavy-light mesons tells us that heavy-light mesons with the same angular momentum $L$ are almost degenerate. The estimate is given how much this degeneracy is broken in our relativistic potential model, and it is analytically shown that expectation values of a commutator between the lowest order Hamiltonian and ${\vec L}^{~2}$ are of the order of $1/m_Q$ with a heavy quark mass $m_Q$. It turns out that nonrelativistic approximation of heavy quark system has a rotational symmetry and hence degeneracy among states with the same $L$. This feature can be tested by measuring higher orbitally and radially excited heavy-light meson spectra for $D/D_s/B/B_s$ in LHCb and forthcoming BelleII.