Quark States Research Articles

Exploiting jet binning to identify the initial state of high-mass resonances

If a new high-mass resonance is discovered at the Large Hadron Collider, model-independent techniques to identify the production mechanism will be crucial to understand its nature and effective couplings to Standard Model particles. We present a powerful and model-independent method to infer the initial state in the production of any high-mass color-singlet system by using a tight veto on accompanying hadronic jets to divide the data into two mutually exclusive event samples (jet bins). For a resonance of several hundred GeV, the jet binning cut needed to discriminate quark and gluon initial states is in the experimentally accessible range of several tens of GeV. It also yields comparable cross sections for both bins, making this method viable already with the small event samples available shortly after a discovery. Theoretically, the method is made feasible by utilizing an effective field theory setup to compute the jet cut dependence precisely and model independently and to systematically control all sources of theoretical uncertainties in the jet binning, as well as their correlations. We use a 750 GeV scalar resonance as an example to demonstrate the viability of our method.

R-matrix calculations for few-quark bound states

The R-matrix method is implemented to study the heavy charm and bottom diquark, triquark, tetraquark, and pentaquarks in configuration space, as the bound states of quark–antiquark, diquark–quark, diquark–antidiquark, and diquark–antitriquark systems, respectively. The mass spectrum and the size of these systems are calculated for different partial wave channels. The calculated masses are compared with recent theoretical results obtained by other methods in momentum and configuration spaces and also by available experimental data.

Investigation of BB̅ four-quark systems using lattice QCD

We investigate BB̅ systems by computing potentials of two static quarks in the presence of two quarks of finite mass using lattice QCD. By solving the Schrodinger equation we check whether these potentials are sufficiently attractive to host bound states. Particular focus is put on the experimentally most promising bottomonium-like tetraquark candidate Zb± with quantum numbers I(JP) = 1(1+).

Comments on the compatibility of thermodynamic equilibrium conditions with lattice propagators

In this paper the compatibility is analyzed of the non-perturbative equations of state of quarks and gluons arising from the lattice with some natural requirements for self-gravitating objects at equilibrium: the existence of an equation of state (namely, the possibility to define the pressure as a function of the energy density), the absence of superluminal propagation and Le Chatelier's principle. It is discussed under which conditions it is possible to extract an equation of state (in the above sense) from the non-perturbative propagators arising from the fits of the latest lattice data. In the quark case, there is a small but non-vanishing range of temperatures in which it is not possible to define a single-valued functional relation between density and pressure. Interestingly enough, a small change of the parameters appearing in the fit of the lattice quark propagator (of around 10~\%) could guarantee the fulfillment of all the three conditions (keeping alive, at the same time, the violation of positivity of the spectral representation, which is the expected signal of confinement). As far as gluons are concerned, the analysis shows very similar results. Whether or not the non-perturbative quark and gluon propagators satisfy these conditions can have a strong impact on the estimate of the maximal mass of quark stars.

Quarkonium production in p–Pb collisions with ALICE

The production of quarkonia, bound states of quark and anti-quark pairs, is intensively studied both experimentally and theoretically. They are ideal probes of the Quark-Gluon Plasma (QGP) formed in heavy-ion collisions. At the beginning of 2013, data from p–Pb collisions at sNN=5.02 TeV have been collected by ALICE, which can be exploited to measure cold nuclear matter (CNM) effects on quarkonium production. These measurements are important in order to disentangle, in Pb–Pb collisions, hot and CNM effects. In this paper final ALICE results on the charmonium and bottomonium production in p–Pb collisions from Run I of the LHC are presented. ALICE measurements are compared to various models of CNM effects and to PHENIX measurements.

Polyakov loop in2+1flavor QCD from low to high temperatures

We study the free energy of a static quark in QCD with 2+1 flavors in a wide temperature region, 116 MeV $< T < $ 5814 MeV, using the highly improved staggered quark (HISQ) action. We analyze the transition region in detail, obtain the entropy of a static quark, show that it peaks at temperatures close to the chiral crossover temperature and also revisit the temperature dependence of the Polyakov loop susceptibilities using gradient flow. We discuss the implications of our findings for the deconfinement and chiral crossover phenomena at physical values of the quark masses. Finally a comparison of the lattice results at high temperatures with the weak-coupling calculations is presented.

Complex spectrum of finite-density lattice QCD with static quarks at strong coupling

We calculate the spectrum of transfer matrix eigenvalues associated with Polyakov loops in finite-density lattice QCD with static quarks. These eigenvalues determine the spatial behavior of Polyakov loop correlations functions. Our results are valid for all values of the gauge coupling in $1+1$ dimensions, and valid in the strong-coupling region for any number of dimensions. When the quark chemical potential $\mu$ is nonzero, the spatial transfer matrix $T_s$ is non-Hermitian. The appearance of complex eigenvalues in $T_s$ is a manifestation of the sign problem in finite-density QCD. The invariance of finite-density QCD under the combined action of charge conjugation $\mathcal{C}$ and complex conjugation $\mathcal{K}$ implies that the eigenvalues of $T_s$ are either real or part of a complex pair. Calculation of the spectrum confirms the existence of complex pairs in much of the temperature-chemical potential plane. Many features of the spectrum for static quarks are determined by a particle-hole symmetry. For $\mu$ small compared to the quark mass $M$, we typically find real eigenvalues for the lowest lying states. At somewhat larger values of $\mu,$ pairs of eigenvalues may form complex-conjugate pairs, leading to damped oscillatory behavior in Polyakov loop correlation functions. However, near $\mu=M$, the low-lying spectrum becomes real again. This is a direct consequence of the approximate particle-hole symmetry at $\mu=M$ for heavy quarks. This behavior of the eigenvalues should be observable in lattice simulations and can be used as a test of lattice algorithms. Our results provide independent confirmation of results we have previously obtained in PNJL models using complex saddle points.

Back reaction effects on the dynamics of heavy probes in heavy quark cloud

We holographically study the effect of back reaction on the hydrodynamical properties of $$ \mathcal{N}=4 $$ strongly coupled super Yang-Mills (SYM) thermal plasma. The back reaction we consider arises from the presence of static heavy quarks uniformly distributed over $$ \mathcal{N}=4 $$ SYM plasma. In order to study the hydrodynamical properties, we use heavy quark as well as heavy quark-antiquark bound state as probes and compute the jet quenching parameter, screening length and binding energy. We also consider the rotational dynamics of heavy probe quark in the back-reacted plasma and analyse associated energy loss. We observe that the presence of back reaction enhances the energy-loss in the thermal plasma. Finally, we show that there is no effect of angular drag on the rotational motion of quark-antiquark bound state probing the back reacted thermal plasma.

Stochastic vacuum of quantum chromodynamics as an environment for color particles

The behavior of quarks is described within approaches used in quantum mechanics and related disciplines (quantum optics and quantum theory of information). The stochastic vacuum of quantum chromodynamics is treated as an environment (closed pool) for color particles (quarks). Their interaction results in a loss of information on the quark color state and consequently in the impossibility of observing it (the confinement of quarks). The processes are described using quantities of the quantum theory of information, such as von Neumann entropy, fidelity, and purity.

Dibaryons with two strange quarks and total spin zero in a constituent quark model

We investigate the symmetry property and construct the wave function of the dibaryon states containing two strange quarks with S=0 in both the flavor SU(3) symmetric and breaking cases. We discuss how the color $\otimes$ isospin $\otimes$ spin states of dibaryon in the symmetry broking case of flavor SU(3) can be extracted from the fully antisymmetric states in flavor SU(3). The stability of the dibaryon against the strong decay into two baryons are then discussed, by using the variational method within a constituent quark model with a confining and color-spin interactions. To compare our results with that from lattice QCD in flavor SU(3) limit, we search for the stable H-dibaryon in a wide range of $\pi$ meson mass. We find that with the given potential, there is no compact six quark dibaryon state in the SU(3) flavor symmetry broken case with realistic quark masses as well as in flavor SU(3) symmetric case in a wide range of quark masses.

Review of QCD, quark–gluon plasma, heavy quark hybrids, and heavy quark state production in p–p and A–A collisions

This is a review of the Quantum Chromodynamics Cosmological Phase Transitions, the quark–gluon plasma, the production of heavy quark states via [Formula: see text]–[Formula: see text] collisions and Relativistic Heavy Ion Collisions (RHIC) using the mixed hybrid theory for the [Formula: see text] and [Formula: see text] states; and the possible detection of the quark–gluon plasma via heavy quark production using RHIC. Recent research on fragmentation for the production of [Formula: see text] mesons is reviewed, as is future theoretical and experimental research on the Collins and Sivers fragmentation functions for pions produced in polarized [Formula: see text]–[Formula: see text] collisions.

Character tables of n-dimensional hyperoctahedral groups and their applications

ABSTRACTWe have shown that powerful matrix-type-based multinomial generators together with combinatorial techniques can be applied to derive the conjugacy classes, irreducible representations and the character tables of n-dimensional hyperoctahedral or hypercube groups of order n! × 2n, which are generalisations of non-rigid molecular theory formulated by Longuet-Higgins. The hyperoctahedral groups appear in the symmetry groups of non-rigid molecules, non-rigid water clusters, and other weakly bound van der Waals complexes that exhibit rapid tunnelling motion among various low-lying surmountable potential energy minima. These groups also have applications in quantum chromodynamics in the classification of states of quarks. The associated combinatorics has applications in enumerations, nuclear spin statistics and NMR spectroscopy. Finally, the groups enhance understanding of chirality in biosystems, that is, the functionality of intrinsically disordered proteins. We have derived the character tables of hyperoctahedral groups of sixth dimension, and techniques have been outlined to generalise for higher dimensions in the form of matrix generators.

The P̅ANDA physics program

The understanding of the QCD in the non-perturbative regime, is one of the key issues to have a complete picture of strong interactions. Recent findings of new and unexpected resonances, with unresolved properties, show that the hadron spectrum is not yet completely understood. This is also underlined by the ongoing discussion on multi- quark states, and on other exotic states with gluonic degrees of freedom. The PANDA experiment, one of the biggest enterprises at the FAIR facility, aims at exploring this field thanks to the gluon rich environment offered by the annihilation of antiprotons. A general overview of the PANDA physics program is given in this paper.

Confining potential of Y-string on the lattice at finite T

The potential due to a system of three static quark (3Q) is studied using SU(3) lattice QCD at finite temperature with Polyakov loops operators. We focused our analysis on the large distance properties of the 3Q potential and found a good fit behavior to the Y-string model formula. In addition to the linearly confining term proportional to the minimal length of the Y-string, we observed that the subleading logarithmic term, which is proportional to Dedekind eta function and accounts for the Y-string's quantum fluctuations, is necessary to reproduce the quark anti-quark string tension of the corresponding mesonic system at finite temperature.

Search for the production of an excited bottom quark decaying to tW in proton-proton collisions at s = 8 $$ \sqrt{s}=8 $$ TeV

A search is presented for a singly produced excited bottom quark (b*) decaying to a top quark and a W boson in the all-hadronic, lepton + jets, and dilepton final states in proton-proton collisions at sqrt(s) = 8 TeV recorded by the CMS experiment at the CERN LHC. Data corresponding to an integrated luminosity of 19.7 inverse femtobarns are used. No significant excess of events is observed with respect to standard model expectations. We set limits at 95% confidence on the product of the b* quark production cross section and its branching fraction to tW. The cross section limits are interpreted for scenarios including left-handed, right-handed, and vector-like couplings of the b* quark and are presented in the two-dimensional coupling plane based on the production and decay coupling constants. The masses of the left-handed, right-handed, and vector-like b* quark states are excluded at 95% confidence below 1390, 1430, and 1530 GeV, respectively, for benchmark couplings. This analysis gives the most stringent limits on the mass of the b* quark to date.

Modelling hybrid stars in quark-hadron approaches

The density in the core of neutron stars can reach values of about 5 to 10 times nuclear matter saturation density. It is, therefore, a natural assumption that hadrons may have dissolved into quarks under such conditions, forming a hybrid star. This star will have an outer region of hadronic matter and a core of quark matter or even a mixed state of hadrons and quarks. In order to investigate such phases, we discuss different model approaches that can be used in the study of compact stars as well as being applicable to a wider range of temperatures and densities. One major model ingredient, the role of quark interactions in the stability of massive hybrid stars is discussed. In this context, possible conflicts with lattice QCD simulations are investigated.

Colour particle states behaviour in the QCD vacuum

The results of an interaction of a quantum state of quark with QCD vacuum, where the latter plays a role of environment, could be treated as decoherence. This may have direct implications for the confinement of quarks phenomenon.The general description and discussion of this process is given. Characteristics from quantum optics and information theory (purity, fidelity, von Neumann entropy) are proposed as means for numerical analysis of the process of interaction of quark colour state with stochastic vacuum.Problems of stability of colour particles motion and order-chaos transitions are briefly discussed. It is shown that there should be a connection between the properties of QCD stochastic vacuum and Higgs boson mass and self interaction coupling constant.The behaviour of squeezed and entangled quantum states, the interaction of colour superpositions and multiparticle states with stochastic QCD vacuum is described. It is shown that it leads to a fully mixed quantum state with equal probabilities for different colours. Decoherence rate is found to be proportional to the product of the distance between colour charges and the time during which this interaction has taken place. I.e. such an interaction seems to lead naturally to confinement of quarks.

Deconfinement and color screening in 2+1 flavor QCD

We discuss the deconfinement an color screening in 2+1 flavor QCD in terms of the free energy of static quarks.

Baryogenesis via mesino oscillations

We propose a new mechanism for baryogenesis at the 1-200 MeV scale. Enhancement of CP violation takes place via interference between oscillations and decays of mesinos--bound states of a scalar quark and antiquark and their CP conjugates. We present the mechanism in a simplified model with four new fundamental particles, with masses between 300 GeV and 10 TeV, and show that some of the experimentally allowed parameter space can give the observed baryon-to-entropy ratio.

Nucleon Properties in AdS/QCD models with several Fock States

We discuss a holographic soft-wall model that consider several Fock states in nucleon description. In our approach nucleon structure is a superposition of a three-valence quark state with high Fock states including an adjustable number of partons (quarks, antiquarks and gluons). 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.