Charged charmonium molecules

We make use of a self-consistent quark-model based study of four-quark charmonium-like states to interpret recent charmonium experimental data. We conclude that there exists a ${D}^{*}{\overline{D}}^{*}$ meson-meson molecule with quantum numbers $({I}^{G}){J}^{PC}=({1}^{\ensuremath{-}}){2}^{++}$. Our study confirms the presence of charged charmonium-like resonances on the excited charmonium spectrum. We find support from recent experimental data by the Belle Collaboration [R. Mizuk et al. (Belle Collaboration), Phys. Rev. D 78, 072004 (2008)]. Confirmation of the experimental data by the Belle Collaboration and the determination of the quantum numbers of the new structures would help in dis…

Diquark-diquark correlations in theS01ΛΛpotential

We derive a $\ensuremath{\Lambda}\ensuremath{\Lambda}$ potential from a chiral constituent quark model that has been successful in describing one, two, and three nonstrange baryon systems. The resulting interaction at low energy is attractive at all distances due to the $\ensuremath{\sigma}$ exchange term. The attraction allows for a slightly bound state just below the $\ensuremath{\Lambda}\ensuremath{\Lambda}$ threshold. No short-range repulsive core is found. We extract the diquark-diquark contribution that turns out to be the most attractive and probable at small distances. At large distances the asymptotic behavior of the $\ensuremath{\Lambda}\ensuremath{\Lambda}$ interaction provides a…

Constituent quark model study of light- and strange-baryon spectra

We investigate the structure of the SU(3) octet and decuplet baryons employing a constituent quark model designed for the study of the baryon-baryon interaction and successfully applied to the meson spectra. The model considers through the interacting potential perturbative, one-gluon exchange, and non-perturbative, boson exchanges and confinement, aspects of the underlying theory, QCD. We solve the three-quark problem by means of the Faddeev method in momentum space. We analyze the effect of the different terms in the interaction and make contact with the use of relativistic kinematics. We find an explanation to the strong contribution of the pseudoscalar forces in the semirelativistic app…

Screened potential and the baryon spectrum

We show that in a quark model scheme the use of a screened potential, suggested by lattice QCD, instead of an infinitely rising one with the interquark distance, provides a more adequate description of the high-energy baryon spectrum. In particular an almost perfect parallelism between the predicted and observed number of states comes out throwing new light about the so-called missing resonance problem.

Hunting exotics

In this work we study the $QQ\bar{n}\bar{n}$ systems from both four--quark and meson--meson molecule formalisms, arriving to consistent conclusions when the proper bases are chosen. These states are interesting as they are thought to be found in experiments soon at LHC or RHIC. Such a source of experimental information will significantly improve our current understanding of charm spectroscopy.

Open-charm meson spectroscopy

We present a theoretical framework that accounts for the new $D_J$ and $D_{sJ}$ mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional $P-$wave quark-antiquark states and four-quark components. The narrowest states are basically $P-$wave quark-antiquark mesons, while the dominantly four-quark states are shifted above the corresponding two-meson threshold, being broad resonances. We study the electromagnetic decay widths as basic tools to scrutiny their nature. The proposed explanation incorporates in a natural way the most recently discovered mesons in charmonium spectroscopy.

The ρ–ω splitting in constituent quark models

Abstract In this Letter we present a solution to describe simultaneously the light isoscalar and isovector vector mesons in constituent quark models. In Ref. [J. Vijande, F. Fernandez, A. Valcarce, J. Phys. G 31 (2005) 481] the q q ¯ spectrum was studied in a generalized constituent quark model constrained by the NN phenomenology and the baryon spectrum. An overall good fit to the available experimental data was obtained. A major problem of this description was the relative position of the vector ω and ρ mesons. The present results improve the description of the isoscalar meson spectroscopy. They should serve as a step forward in distinguishing conventional quark model mesons from exotic st…

Neutral baryonic systems with strangeness

We review the status as regards the existence of three- and four-body bound states made of neutrons and $\Lambda$ hyperons. For interesting cases, the coupling to neutral baryonic systems made of charged particles of different strangeness has been addressed. There are strong arguments showing that the $\Lambda nn$ system has no bound states. $\Lambda\Lambda nn$ strong stable states are not favored by our current knowledge of the strangeness $-1$ and $-2$ baryon-baryon interactions. However, a possible $\Xi^- t$ quasibound state decaying to $\Lambda\Lambda nn$ might exist in nature. Similarly, there is a broad agreement about the nonexistence of $\Lambda\Lambda n$ bound states. However, the …

$b\bar b$ DESCRIPTION WITH A SCREENED POTENTIAL

Recent lattice QCD calculations suggest a rather abrupt transition in the confinig potential from a linear to a constant behavior. We analyze the effects of such a fast deconfinement in the simplest non-relativistic system, bottomonium.

Towards the understanding of the meson spectra

We present a quark-quark interaction for the complete study of the meson spectra, from the light to the heavy sector. We compare the quark model predictions against well-established $q\bar q$ experimental data. This allows to identify discrepancies between quark model results and experiment that may signal physics beyond conventional hadron spectroscopy.

Exotic bcq¯q¯ four-quark states

We carry out a systematic study of exotic $Q{Q}^{\ensuremath{'}}\overline{q}\overline{q}$ four-quark states containing distinguishable heavy flavors, $b$ and $c$. Different generic constituent models are explored in an attempt to extract general conclusions. The results are robust, predicting the same sets of quantum numbers as the best candidates to lodge bound states independently of the model used, the isoscalar ${J}^{P}={0}^{+}$ and ${J}^{P}={1}^{+}$ states. The first state would be strong and electromagnetic-interaction stable, while the second would decay electromagnetically to $\overline{B}D\ensuremath{\gamma}$. Isovector states are found to be unbound, preventing the existence of ch…

Strange tribaryons

We use two-body potentials derived from a constituent quark cluster model to analyze the bound-state problem of the $\Sigma NN$ system. The observables of the two-body subsystems, $NN$ and $\Sigma N$, are well reproduced. We do not find $\Sigma NN$ bound states, but there are two attractive channels with a resonance close above the three-body threshold. These channels are the $(I,J)=(1,1/2)$ and $(0,1/2)$, their quantum numbers, widths and energy ordering consistent with the recently measured strange tribaryons from the $^{4}{\rm He}(K_{{\rm stopped}}^{-},N)$ reactions in the KEK PS E471 experiment.

Maximal isospin few-body systems of nucleons and $\Xi$ hyperons

By using local central Yukawa-type interactions that reproduce the low-energy parameters of the latest updates of the Nijmegen ESC08c potentials we show that the $N\Xi$, $NN\Xi$, $N\Xi\Xi$ and $NN\Xi\Xi$ systems with maximal isospin are bound. Since in these states the strong decay $N\Xi\to\Lambda\Lambda$ is forbidden by isospin conservation, these strange few-body systems will be stable under the strong interaction. These results may suggest that other states with different number of $N$'s and $\Xi$'s in the maximal isospin channel could also be bound.

Hyperspherical harmonic study of identical-flavor four-quark systems

4 pages.-- ISI Article Identifier: 000248297600103.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0610287

Doubly charmed exotic mesons: A gift of nature?

Article history: We study doubly charmed exotic states by solving the scattering problem of two D mesons. Our results point to the existence of a stable isoscalar doubly charmed meson with quantum numbers (I) J P = (0)1 + . We perform a thorough comparison to the results obtained within the hyperspherical harmonic formalism. Such exotic states could be measured at LHC and RHIC. Their experimental observation would,

Production of exotic tetraquarks QQq¯q¯ in heavy-ion collisions at the LHC

We investigate the production of exotic tetraquarks, $QQ\overline{q}\overline{q}\ensuremath{\equiv}{T}_{QQ}$ ($Q=c$ or $b$ and $q=u$ or $d$), in relativistic heavy-ion collisions using the quark coalescence model. The ${T}_{QQ}$ yield is given by the overlap of the density matrix of the constituents in the emission source with the Wigner function of the produced tetraquark. The tetraquark wave function is obtained from exact solutions of the four-body problem using realistic constituent models. The production yields are typically one order of magnitude smaller than previous estimations based on simplified wave functions for the tetraquarks. We also evaluate the consequences of the partial r…

A consistent study of the the low energy baryon spectrum and the nucleon-nucleon interaction within the chiral quark model

By solving the Schr\"{o}dinger equation for the three-quark system in the hyperspherical harmonic approach, we have studied the low energy part of the nucleon and $\Delta$ spectra using a quark-quark interaction which reproduces the nucleon-nucleon phenomenology. The quark-quark hamiltonian considered includes, besides the usual one-gluon exchange, pion and sigma exchanges generated by the chiral symmetry breaking. The baryonic spectrum obtained is reasonable and the resulting wave function gives consistency to the ansatz used in the two baryon system.

Quark-model description of the NN*(1440) potential

We derive a $NN^*$(1440) potential from a non-relativistic quark-quark interaction and a chiral quark cluster model for the baryons. By making use of the Born-Oppenheimer approximation we examine the most important features of this interaction in comparison to those obtained from meson-exchange models.

ON THE NATURE OF THE X(3872)

We present recent studies of charmonium multiquark states. We use different interacting models and numerical methods to study deeply bound four-quark states and meson-meson molecules. No deeply bound four-quark states are found in our analysis. A nice description of the X(3872) is obtained as a $D\bar{D}^*-J/\Psi\omega$ coupled channel state.

Basics of doubly heavy tetraquarks

We outline the most important results regarding the stability of doubly heavy tetraquarks $QQ\bar q\bar q$ with an adequate treatment of the four-body dynamics. We consider both color-mixing and spin-dependent effects. Our results are straightforwardly applied to the case of all-heavy tetraquarks $QQ\bar Q\bar Q$. We conclude that the stability is favored in the limit $M_Q/m_q \gg 1$ pointing to the stability of the $bb\bar u\bar d$ state and the instability of all-heavy tetraquarks.

Multiquark description of theDsJ(2860)andDsJ(2700)

Within a theoretical framework that accounts for all open-charm mesons, including the ${D}_{0}^{*}(2308)$, the ${D}_{sJ}^{*}(2317)$, and the ${D}_{sJ}(2460)$, we analyze the structure and explore possible quantum number assignments for the ${D}_{sJ}(2860)$ and the ${D}_{sJ}(2700)$ mesons reported by BABAR and Belle Collaborations. The open-charm sector is properly described if considered as a combination of conventional quark-antiquark states and four-quark components. All negative parity and ${2}^{+}$ states can be understood in terms only of $q\overline{q}$ components, however the description of the ${0}^{+}$ and ${1}^{+}$ mesons is improved whenever the mixing between two- and four-quark…

Understanding open-charm mesons

We present a theoretical framework that accounts for the new $D_J$ and $D_{sJ}$ mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional $P-$wave quark-antiquark states and four-quark components. The narrowest states are basically $P-$wave quark-antiquark mesons, while the dominantly four-quark states are shifted above the corresponding two-meson threshold. We study the electromagnetic decay widths as basic tools to scrutiny their nature.

Constituent-quark model description of triply heavy-baryon nonperturbative lattice QCD data

This paper provides results for the spectra of triply charmed and bottom baryons based on a constituent quark model approach. We take advantage of the assumption that potential models are expected to describe triply heavy baryons to a similar degree of accuracy as the successful results obtained in the charmonium and bottomonium sectors. The high precision calculation of the ground state and positive and negative parity excited states recently reported by nonperturbative lattice QCD provides us with a unique opportunity to confront model predictions with data. This comparison may also help to build a bridge between two difficult to reconcile lattice QCD results, namely, the lattice SU(3) QC…

Hall–Post inequalities: Review and application to molecules and tetraquarks

A review is presented of the Hall–Post inequalities that give lower-bounds to the ground-state energy of quantum systems in terms of energies of smaller systems. New applications are given for systems experiencing both a static source and inner interactions, as well as for hydrogen-like molecules and for tetraquarks in some quark models. In the latter case, the Hall–Post inequalities constrain the possibility of deeply-bound exotic mesons below the threshold for dissociation into two quark–antiquark mesons. We also emphasize the usefulness of the Hall–Post bounds in terms of 3-body energies when some 2-body subsystems are ill defined or do not support any bound state.

Heavy Meson Description with a Screened Potential

We perform a quark model calculation of the $b\bar{b}$ and $c\bar{c}$ spectra from a screened funnel potential form suggested by unquenched lattice calculations. A connection between the lattice screening parameter and an effective gluon mass directly derived from QCD is established. Spin-spin energy splittings, leptonic widths and radiative decays are also examined providing a test for the description of the states.

QCD Confinement and the Meson Spectrum

From QCD and lattice calculations two specific forms of quark confining potential, a strict linear and a screened linear confinement, come out. Both forms of the potential, implemented by the one gluon exchange interaction, are applied to the description of heavy quarkonia: cc and bb. Applications to light hadrons, mesons and baryons, are also commented.

Extended van Royen-Weisskopf formalism for lepton-antilepton meson decay widths within non-relativistic quark models

The classical van Royen-Weisskopf formula for the decay width of a meson into a lepton-antilepton pair is modified in order to include non-zero quark momentum contributions within the meson as well as relativistic effects. Besides, a phenomenological electromagnetic density for quarks is introduced. The meson wave functions are obtained from two different models: a chiral constituent quark model and a quark potential model including instanton effects. The modified van Royen-Weisskopf formula is found to improve systematically the results for the widths, giving an overall good description of all known decays.

Understanding the Low Energy Hadron Spectrum in a Chiral Quark Cluster Model

The low energy N and Δ spectra are studied by means of a chiral quark cluster model. We solve the Schrodinger equation in the hyperspherical harmonic approach. The interacting potential includes Goldstone boson exchanges besides the usual one-gluon exchange. The predicted baryonic spectrum is quite reasonable. However, if consistency with the two-baryon sector is required, the observed inversion of the positive and negative parity excitations of the nucleon cannot be obtained. Alternative solutions are discussed.

Towards an understanding of heavy baryon spectroscopy

The recent observation at CDF and D0 of $\Sigma_b$, $\Sigma^*_b$ and $\Xi_b$ baryons opens the door to the advent of new states in the bottom baryon sector. The states measured provide sufficient constraints to fix the parameters of phenomenological models. One may therefore consistently predict the full bottom baryon spectra. For this purpose we have solved exactly the three-quark problem by means of the Faddeev method in momentum space. We consider our guidance may help experimentalists in the search for new bottom baryons and their findings will help in constraining further the phenomenological models. We identify particular states whose masses may allow to discriminate between the dynam…

Towards a Unified Description of the Baryon Spectrum and the Baryon-Baryon Interaction within a Potential Model Scheme

We study the low energy part of the nucleon and ∆ spectra by solving the Schrodinger equation for the three-quark system in the hyperspherical harmonic approach. The quark-quark hamiltonian considered includes, besides the usual one-gluon exchange, pion and sigma exchanges generated by the chiral symmetry breaking This quark-quark potential reproduces, in a Resonating Group Method calculation, the nucleon-nucleon scattering phase shifts and the deuteron properties. The baryonic spectrum obtained is quite reasonable and the resulting wave function is consistent with the ansatz used in the two baryon system.

πB8B8andσB8B8couplings from a chiral quark potential model

From an SU(2)$\ensuremath{\bigotimes}$SU(2) chiral quark potential model incorporating spontaneous chiral symmetry breaking the asymptotic $\ensuremath{\pi}$ and $\ensuremath{\sigma}$ exchange pieces of the $\mathit{NN}$ potential are generated. From them the $\ensuremath{\pi}\mathit{NN}$ and $\ensuremath{\sigma}\mathit{NN}$ coupling constants can be extracted. The generalization to SU(3)$\ensuremath{\bigotimes}$SU(3) allows for a determination of $\ensuremath{\pi}{B}_{8}{B}_{8}$ and $\ensuremath{\sigma}{B}_{8}{B}_{8}$ coupling constants according to exact SU(3) hadron symmetry. The implementation of the values of the couplings at ${Q}^{2}=0$ provided by QCD sum rules and/or phenomenology m…

A microscopic N N → N N*(1440) potential

By means of a NN → N N* (1440) transition potential derived in a parameter-free way from a quark-model based N N potential, we determine simultaneously the πN N*(1440) and σ N N* (1440) coupling constants. We also present a study of the target Roper excitation diagram contributing to the p(d,d’) reaction.

HEAVY HADRON SPECTROSCOPY: A QUARK MODEL PERSPECTIVE

We present recent results of hadron spectroscopy and hadron hadron interaction from the perspective of constituent quark models. We pay special attention to the role played by higher-order hock space components in the hadron spectra and the connection of this extension with the hadron-hadron interaction. The main goal of our description is to obtain a coherent understanding of the low-energy hadron phenomenology without enforcing any particular model, to constrain its characteristics and learn about the low-energy realization of the theory.

Stability of multiquarks in an improved flip-flop model of confinement

We review some recent studies on the string model of confinement inspired by the strong-coupling regime of QCD and its application to exotic multiquark configurations. This includes two quarks and two antiquarks, four quarks and one antiquark, six quarks, and three quarks and three antiquarks with a careful treatment of the corresponding few-body problem.

Molecular and compact four-quark states

5th International Conference on Quarks and Nuclear Physics (QNP09). Inst High Energy Phys Chinese Acad Sci, Beijing, PEOPLES R CHINA, SEP 21-25, 2009

Too many Xʼs, Yʼs and Zʼs?

Abstract A large number of new states have been reported during the last few years in charmonium spectroscopy above the charmed meson production threshold. They have been called X ʼs, Y ʼs, and Z ʼs. We reflect on the influence of thresholds on heavy meson spectroscopy comparing different flavor sectors and quantum numbers. The validity of a quark-model picture above open-flavor thresholds would severely restrict the number of channels that may lodge meson–meson molecules.

Stability of multiquarks in a simple string model

A simple string model inspired by the strong-coupling regime of Quantum ChromoDynamics is used as a potential for studying the spectrum of multiquark systems with two quarks and two antiquarks, with a careful treatment of the four-body problem. It is found that the ground state is stable, lying below the threshold for dissociation into two isolated mesons.

Symmetry patterns in the (N, Delta) spectrum

We revise the role played by symmetry in the study of the low-lying baryon spectrum and comment on the difficulties when trying to generalize the symmetry pattern to higher energy states. We show that for the $(N,\Delta)$ part such a generalization is plausible allowing the identification of spectral regularities and the prediction of until now non-identified resonances.

Spectral patterns in the nonstrange baryon spectrum

We extract, from a quark model potential that reproduces the number and ordering of nonstrange baryonic resonances up to 2.3 GeV, the quantum numbers for the dominant configurations in the ground and first non-radial excited states. From the pattern of quantum numbers we identify, from data, spectral regularities that allow us to predict the expected high spin low-lying spectrum from 2.3 to 3.0 GeV. $N-\Delta$ degeneracies and $N$ parity doublets showing up can be interpreted in terms of a simple dynamics.

Quark-model based study of the triton binding energy

The three-nucleon bound state problem is studied employing a nucleon-nucleon potential obtained from a basic quark-quark interaction in a five-channel Faddeev calculation. The obtained triton binding energy is comparable to those predicted by conventional models of the $NN$ force.

Pentaquarks with anticharm or beauty revisited

We use a constituent model to analyze the stability of pentaquark $\bar Q qqqq$ configurations with a heavy antiquark $\bar c$ or $\bar b$, and four light quarks $uuds$, $ddsu$ or $ssud$. The interplay between chromoelectric and chromomagnetic effects is not favorable, and, as a consequence, no bound state is found below the lowest dissociation threshold.

Tetraquark Spectroscopy: A Symmetry Analysis

We present a detailed analysis of the symmetry properties of a four-quark wave function and its solution by means of a variational approach for simple Hamiltonians. We discuss several examples in the light and heavy-light meson sector.

Doubly heavy baryon spectra guided by lattice QCD

This paper provides results for the ground state and excited spectra of three-flavored doubly heavy baryons, $bcn$ and $bcs$. We take advantage of the spin-independent interaction recently obtained to reconcile the lattice SU(3) QCD static potential and the results of nonperturbative lattice QCD for the triply heavy baryon spectra. We show that the spin-dependent potential might be constrained on the basis of nonperturbative lattice QCD results for the spin splittings of three-flavored doubly heavy baryons. Our results may also represent a challenge for future lattice QCD work, because a smaller lattice error could help in distinguishing between different prescriptions for the spin-dependen…

B meson spectroscopy

We study the $B$ meson spectroscopy allowing the mixture of conventional $P$ wave quark-antiquark states and four-quark components. A similar picture was used to describe the new $D_J$ and $D_{sJ}$ open charm mesons. The four-quark components shift the masses of some positive parity $B_{sJ}$ states below their corresponding isospin preserving two-meson threshold and therefore they are expected to be narrow. Electromagnetic decay widths are analyzed.

Breaking Symmetry Effects on Heavy Tetraquarks

In this contribution we present symmetry arguments that can be applied to study the stability of four-quark systems with two different masses. The role played by different symmetry breaking effects and the non-Abelian algebra of color forces is discussed in detail. In the particular case of hidden-flavor all-heavy four-quark states, QQ (Q) over bar(Q) over bar, the system becomes unstable for standard color-additive models. Differences and similarities between Qq (Q) over bar(q) over bar and QQ (q) over bar(q) over bar configurations are presented. In the latter case, its stability when the mass ratio M/m increases was established almost forty years ago. In the former case, we find a kind o…

Heavy baryon spectroscopy with relativistic kinematics

We present a comparative Faddeev study of heavy baryon spectroscopy with nonrelativistic and relativistic kinematics. We show results for different standard hyperfine interactions with both kinematics in an attempt to learn about the light quark dynamics. We highlight the properties of particular states accessible in nowadays laboratories that would help in discriminating between different dynamical models. The advance in the knowledge of light quark dynamics is a key tool for the understanding of the existence of exotic hadrons.

Stability of hexaquarks in the string limit of confinement

The stability of systems containing six quarks or antiquarks is studied within a simple string model inspired by the strong-coupling regime of quantum chromodynamics and used previously for tetraquarks and pentaquarks. We discuss both six-quark $(q^6)$ and three-quark--three-antiquark $ (q^3\bar q{}^3)$ states. The quarks are assumed to be distinguishable and thus not submitted to antisymmetrization. It is found that the ground state of $(q^6)$ is stable against dissociation into two isolated baryons. For the case of $ (q^3\bar q{}^3)$, our results indicate the existence of a bound state very close to the threshold. The investigations are extended to $(q^3Q^3)$ and $(Q^3\bar q^3)$ systems w…

Too many $X's$, $Y's$ and $Z's$?

Heavy meson spectroscopy above open flavor thresholds has become a challenge both from the experimental and theoretical points of view. Experimentally, several signals have been interpreted as meson resonances with unusual properties; theoretically, such signals may be identified with meson-meson molecules or compact multiquark structures. We analyze the influence of thresholds on heavy meson spectroscopy comparing different flavor sectors and quantum numbers. The validity of a quark-model picture above open-flavor thresholds would severely restrict the number of channels that may lodge multiquark structures as meson-meson molecules.

Very Heavy Flavored Dibaryons

We explore the possibility of very heavy dibaryons with three charm quarks and three beauty quarks, $bbbccc$, using a constituent model which should drive to the correct solution in the limit of hadrons made of heavy quarks. The six-body problem is treated rigorously, in particular taking into account the orbital, color and spin mixed-symmetry components of the wave function. Unlike a recent claim based on lattice QCD, no bound state is found below the lowest dissociation threshold.

ΛNNandΣNNsystems at threshold

We calculate the hypertriton binding energy and the $\ensuremath{\Lambda}d$ and $\ensuremath{\Sigma}d$ scattering lengths using baryon-baryon interactions obtained from a chiral constituent quark model. We study consistently the $\ensuremath{\Lambda}\mathit{NN}$ and $\ensuremath{\Sigma}\mathit{NN}$ systems by analyzing the effect of the $\ensuremath{\Sigma}\ensuremath{\leftrightarrow}\ensuremath{\Lambda}$ conversion. Our interactions correctly predict the hypertriton binding energy. The $(I,J)=(0,3/2)$ $\ensuremath{\Lambda}\mathit{NN}$ channel is also attractive and it might have a bound state. From the condition of nonexistence of a (0,3/2) $\ensuremath{\Lambda}\mathit{NN}$ bound state, an…

Quark-model study of the hadron structure and the hadron-hadron interaction

Recent results of hadron spectroscopy and hadron-hadron interaction within a quark model framework are reviewed. Higher order Fock space components are considered based on new experimental data on low-energy hadron phenomenology. The purpose of this study is to obtain a coherent description of the low-energy hadron phenomenology to constrain QCD phenomenological models and try to learn about low-energy realizations of the theory.

Docc¯nn¯bound states exist?

The four-quark system $c\overline{c}n\overline{n}$ is studied in the framework of the constituent quark model. Using different types of quark-quark potentials, we solve the four-body Schr\"odinger equation by means of the hyperspherical harmonic formalism. Exploring the low laying ${J}^{\mathrm{PC}}$ states for different isospin configurations no four-quark bound states have been found. Of particular interest is the possible four-quark structure of the $X(3872)$. We rule out the possibility that this particle is a compact tetraquark system, unless additional correlations, either in the form of diquarks or at the level of the interacting potential, not considered in simple quark models do co…

Meson-baryon threshold effects in the light-quark baryon spectrum

We argue that selected $S$ wave meson-baryon channels may play a key role to match poor baryon mass predictions from quark models with data. The identification of these channels with effective inelastic channels in data analysis allows to derive a prescription which could improve the extraction and identification of baryon resonances.

On the existence of exotic and non-exotic multiquark meson states

To obtain an exact solution of a four-body system containing two quarks and two antiquarks interacting through two-body terms is a cumbersome task that has been tackled with more or less success during the last decades. We present an exact method for the study of four-quark systems based on the hyperspherical harmonics formalism that allows us to solve it without resorting to further approximations, like for instance the existence of diquark components. We apply it to systems containing two heavy and two light quarks using different quark-quark potentials. While $QQ\bar n \bar n$ states may be stable in nature, the stability of $Q\bar Qn \bar n$ states would imply the existence of quark cor…

Multiquark description of the D-sJ(2860) and D-sJ(2700)

Within a theoretical framework that accounts for all open-charm mesons, including the D-0*(2308), the D-sJ*(2317), and the D-sJ(2460), we analyze the structure and explore possible quantum number assignments for the D-sJ(2860) and the D-sJ(2700) mesons reported by BABAR and Belle Collaborations. The open-charm sector is properly described if considered as a combination of conventional quark-antiquark states and four-quark components. All negative parity and 2(+) states can be understood in terms only of q (q) over bar components, however the description of the 0(+) and 1(+) mesons is improved whenever the mixing between two- and four-quark configurations is included. We analyze all possible…

Quark-model hadron structure

We review some selected recent results on hadron spectroscopy and related theoretical studies based on constituent quark models.

CHARMONIUM: X(3872) AND BEYOND

We analyze the spectrum of charmonium above the threshold for the production of D mesons. Several recent intriguing experimental data have reopen the interest on charmonium spectroscopy and they deserve an special attention. We focus our study on the X(3872) and the possible existence of charged states contributing to the spectrum of charmonium

Effect of relativistic kinematics on the stability of multiquarks

We discuss whether the bound nature of multiquark states in quark models could benefit from relativistic effects on the kinetic energy operator. For mesons and baryons, relativistic corrections to the kinetic energy lead to lower energies, and thus call for a retuning of the parameters of the model. For multiquark states, as well as their respective thresholds, a comparison is made of the results obtained with non-relativistic and relativistic kinetic energy. It is found that the binding energy is lower in the relativistic case. In particular, $QQ\bar q\bar q$ tetraquarks with double heavy flavor become stable for a larger ratio of the heavy to light quark masses; and the all-heavy tetraqua…

ΛNNandΣNNsystems at threshold. II. The effect ofDwaves

Using the two-body interactions obtained from a chiral constituent quark model, we study allN N andN N states with I = 0, 1, 2a ndJ = 1/2, 3/2 at threshold, taking into account all three-body configurations with S and D wave components. We constrain further the limits for theN spin-triplet scattering length a1/2,1 .U sing the hypertriton binding energy, we find a narrow interval for the possible values of theN spin-singlet scattering length a1/2,0. We find that theN N system has a quasibound state in the (I,J ) = (1, 1/2) channel very near threshold with a width of about 2.1 MeV.

Chiral quark cluster model approach to the baryon spectra and the NN interaction

Nature of the light scalar mesons

Despite the apparent simplicity of meson spectroscopy, light scalar mesons cannot be accommodated in the usual $q\bar q$ structure. We study the description of the scalar mesons below 2 GeV in terms of the mixing of a chiral nonet of tetraquarks with conventional $q\bar q$ states. A strong diquark-antidiquark component is found for several states. The consideration of a glueball as dictated by quenched lattice QCD drives a coherent picture of the isoscalar mesons.

Stable heavy pentaquarks in constituent models

It is shown that standard constituent quark models produce $(\bar c c qqq)$ hidden-charm pentaquarks, where $c$ denotes the charmed quark and $q$ a light quark, which lie below the lowest threshold for spontaneous dissociation and thus are stable in the limit where the internal $\bar c c$ annihilation is neglected. The binding is a cooperative effect of the chromoelectric and chromomagnetic components of the interaction, and it disappears in the static limit with a pure chromoelectric potential. Their wave function contains color sextet and color octet configurations for the subsystems and can hardly be reduced to a molecular state made of two interacting hadrons. These pentaquark states co…

Tetraquarks in a chiral constituent-quark model

We analyze the possibility of heavy-light tetraquark bound states by means of a chiral constituent quark model. The study is done in a variational approach. Special attention is paid to the contribution given by the different terms of the interacting potential and also to the role played by the different color channels. We find a stable state for both $qq\bar{c}\bar{c}$ and $qq\bar{b}\bar{b}$ configurations. Possible decay modes of these structures are analyzed.

Are there compact heavy four-quark bound states?

6 pages, 1 figure.-- PACS nrs.: 12.39.Jh; 14.40.Lb.-- ISI Article Identifier: 000251327200050.-- ArXiv pre-print available at: http://arxiv.org/abs/0710.2516

Constituent quark model study of the meson spectra

The $q\bar q$ spectrum is studied in a generalized constituent quark model constrained in the study of the $NN$ phenomenology and the baryon spectrum. An overall good fit to the available experimental data is obtained. A detailed analysis of all sectors from the light-pseudoscalar and vector mesons to bottomonium is performed paying special attention to the existence and nature of some non well-established states. These results should serve as a complementary tool in distinguishing conventional quark model mesons from glueballs, hybrids or multiquark states.

Probabilities in nonorthogonal basis: Four--quark systems

Four-quark states may exist as colorless meson-meson molecules or compact systems with two-body colored components. We derive an analytical procedure to expand an arbitrary four-quark wave function in terms of nonorthogonal color singlet-singlet vectors. Using this expansion we develop the necessary formalism to evaluate the probability of physical components with an arbitrary four-quark wave function. Its application to characterize bound and unbound four-quark states as meson-meson, molecular, or compact systems is discussed

Multiquark structures in heavy-light meson systems

We look for possible signatures of multiquark structures in the heavy-light meson spectra. The controversial D s 0 ∗ ( 2317 ) and D s 1 ∗ ( 2460 ) states are properly described if considered as a mixture of conventional P-wave q q ¯ and four-quark components. The recently discovered D s J ∗ ( 2860 ) appears as the orthogonal partner of the D s 0 ∗ ( 2317 ) . Similar structures are predicted in the B s sector. We also consider the possible existence of isolated I = 1 four-quark resonances and we argue that their existence can disentangle the ϒ ( n S ) → ϒ ( m S ) π π decay puzzle.

Unraveling the pattern of the XYZ mesons

We present a plausible mechanism for the origin of the $XYZ$ mesons in the heavy meson spectra within a standard quark-model picture. We discuss the conditions required for the existence of four--quark bound states or resonances contributing to the heavy meson spectra, being either compact or molecular. We concentrate on charmonium and bottomonium spectra, where several new states, difficult to understand as simple quark-antiquark pairs, have been reported by different experimental collaborations. The pivotal role played by entangled meson-meson thresholds is emphasized.

Nonlocal calculation for nonstrange dibaryons and tribaryons

We study the possible existence of nonstrange dibaryons and tribaryons by solving the bound-state problem of the two- and three-body systems composed of nucleons and deltas. The two-body systems are $NN$, $N\Delta$, and $\Delta\Delta$, while the three-body systems are $NNN$, $NN\Delta$, $N\Delta\Delta$, and $\Delta\Delta\Delta$. We use as input the nonlocal $NN$, $N\Delta$, and $\Delta\Delta$ potentials derived from the chiral quark cluster model by means of the resonating group method. We compare with previous results obtained from the local version based on the Born-Oppenheimer approximation.

DOUBLY CHARMED MESONS

Doubly charmed mesons are studied within a quark model framework. We solve the four-quark Schor\"dinger equation by means of a variational approach by using different interacting potentials. Our results point to the existence of a stable isoscalar doubly charmed four-quark meson with quantum numbers $J^P=1^+$.

Four-quark spectroscopy within the hyperspherical formalism

We present a generalization of the hyperspherical harmonic formalism to study systems made of quarks and antiquarks of the same flavor. This generalization is based on the symmetrization of the $N-$body wave function with respect to the symmetric group using the Barnea and Novoselsky algorithm. The formalism is applied to study four-quark systems by means of a constituent quark model successful in the description of the two- and three-quark systems. The results are compared to those obtained by means of variational approaches. Our analysis shows that four-quark systems with exotic $0^{+-}$ and non-exotic $2^{++}$ quantum numbers may be bound independently of the mass of the quark. $2^{+-}$ …

String dynamics and metastability of fully-heavy tetraquarks

Multiquark states have been advocated to explain recent experimental data in the heavy-light sector, and there are already speculations about multiquarks containing only heavy quarks and antiquarks. With a rigorous treatment of the four-body problem in current quark models, full-charm $(cc\bar c\bar c)$ and full-beauty $(bb\bar b\bar b)$ tetraquarks are found to be unbound. Thus their stability should rely on more subtle effects that are not included in the simple picture of constituent quarks. The case of $(bc\bar b\bar c)$ might be more favorable if the naive color-additive model of confinement is replaced by a string-inspired interaction.

Screened potential and quarkonia properties at high temperatures

We perform a quark model calculation of the quarkonia b (b) over bar and c (c) over bar spectra using smooth and sudden string breaking potentials. The screening parameter is scale dependent and can be related to an effective running gluon mass that has a finite infrared fixed point. A temperature dependence for the screening mass is motivated by lattice QCD simulations at finite temperature. Qualitatively different results are obtained for quarkonia properties close to a critical value of the deconfining temperature when a smooth or a sudden string breaking potential is used. In particular, with a sudden string breaking potential quarkonia radii remain almost independent of the temperature…

Few-body insights of multiquark exotic hadrons

In this contribution we discuss the adequate treatment of the $4-$ and $5-$body dynamics within a constituent quark framework. We stress that the variational and Born-Oppenheimer approximations give energies rather close to the exact ones, while the diquark approximation might be rather misleading. Hall-Post inequalities provide very useful lower bounds that exclude possible stable states for some mass ratios and color wave functions.

Faddeev study of heavy baryon spectroscopy

16 pages, 3 figures.-- PACS nrs.: 12.39.Jh, 12.39.Pn, 14.20.-c.-- ISI Article Identifier: 000246249100015.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0703257

Adiabaticity and color mixing in tetraquark spectroscopy

We revisit the role of color mixing in the quark model calculation of tetraquark states, and compare simple pairwise potentials to more elaborate string models with three-and four-body forces. We attempt to disentangle the improved dynamics of confinement from the approximations made in the treatment of the internal color degrees of freedom.

Spectroscopy, lifetime and decay modes of the Tbb− tetraquark

Abstract We present the first full-fledged study of the flavor-exotic isoscalar T b b − ≡ b b u ¯ d ¯ tetraquark with spin and parity J P = 1 + . We report accurate solutions of the four-body problem in a quark model, characterizing the structure of the state as a function of the ratio M Q / m q of the heavy to light quark masses. For such a standard constituent model, T b b − lies approximately 150 MeV below the strong decay threshold B − B ⁎ ¯ 0 and 105 MeV below the electromagnetic decay threshold B − B ¯ 0 γ . We evaluate the lifetime of T b b − , identifying the promising decay modes where the tetraquark might be looked for in future experiments. Its total decay width is Γ ≈ 87 × 10 − …

NN Interaction in Chiral Constituent Quark Models

We review the actual state in the description of the nucleon-nucleon (NN) interaction by means of chiral constituent quark models. We present a series of relevant features that are nicely explained within the quark model framework.

Four-quark stability

The physics of charm has become one of the best laboratories exposing the limitations of the naive constituent quark model and also giving hints into a more mature description of meson spectroscopy, beyond the simple quark--antiquark configurations. In this talk we review some recent studies of multiquark components in the charm sector and discuss in particular exotic and non-exotic four-quark systems, both with pairwise and many-body forces.

Lifetime and dominant decay modes of the tetraquark with double beauty bbu¯d¯

Charmonium spectroscopy above thresholds

We present a systematic and self-consistent analysis of four-quark charmonium states and applied it to study compact four-quark systems and meson-meson molecules. Our results are robust and should serve to clarify the situation of charmonium spectroscopy above the threshold production of charmed mesons.

Few-body quark dynamics for doubly heavy baryons and tetraquarks

We discuss the adequate treatment of the 3- and 4-body dynamics for the quark model picture of double-charm baryons and tetraquarks. We stress that the variational and Born-Oppenheimer approximations give energies very close to the exact ones, while the diquark approximation might be rather misleading. The Hall-Post inequalities also provide very useful lower bounds that exclude the possibility of stable tetraquarks for some mass ratios and some color wave functions.

Spectroscopy of doubly charmed baryons

We study the mass spectrum of baryons with two and three charmed quarks. For double charm baryons the spin splitting is found to be smaller than standard quark-model potential predictions. This splitting is not influenced either by the particular form of the confining potential or by the regularization taken for the contact term of the spin-spin potential. We consistently predict the spectra for triply charmed baryons.

Microscopic description of the nucleon- Delta interaction in the quark cluster model.

By using a nonrelativistic quark cluster model to describe baryonic systems, we generate a nucleon-{Delta} potential from the elementary interaction between constituents. The basic quark-quark potential used provides, when applied to the nucleon-nucleon system, an adequate description of the scattering phase shifts, the deuteron properties and the nonstrange baryonic spectroscopy. Special attention is paid to the short-range behavior of the interaction and its connection to the quark Pauli principle. This establishes a conceptual difference with meson-exchange models where the interaction, due to the lack of data, is not even well defined.

Exotic meson-meson molecules and compact four-quark states

PACS numbers: 12.39.Jh, 14.40.Lb, 21.45.-v, 31.15.xj.-- ArXiv pre-print avaible at: http://arxiv.org/abs/0903.2949v1

Heavy-baryon quark model picture from lattice QCD

The ground state and excited spectra of baryons containing three identical heavy quarks, $b$ or $c$, have been recently calculated in nonperturbative lattice QCD. The energy of positive and negative parity excitations has been determined with high precision. Lattice results constitute a unique opportunity to learn about the quark-confinement mechanism as well as elucidating our knowledge about the nature of the strong force. We analyze the nonperturbative lattice QCD results by means of heavy-quark static potentials derived using SU(3) lattice QCD. We make use of different numerical techniques for the three-body problem.

Hyperspherical harmonic formalism for tetraquarks

5 pages, 2 tables.-- ISI Article Identifier: 000250926800050.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0610124

Effect of higher orbital angular momenta in the baryon spectrum

We have performed a Faddeev calculation of the baryon spectrum for the chiral constituent quark model including higher orbital angular momentum states. We have found that the effect of these states is important, although a description of the baryon spectrum of the same quality as the one given by including only the lowest-order configurations can be obtained. We have studied the effect of the pseudoscalar quark-quark interaction on the relative position of the positive- and negative-parity excitations of the nucleon as well as the effect of varying the strength of the color-magnetic interaction.

Quark-model study of few-baryon systems

We review the application of non-relativistic constituent quark models to study one, two and three non-strange baryon systems. We present results for the baryon spectra, potentials and observables of the NN, N$\Delta$, $\Delta\Delta$ and NN$^*(1440)$ systems, and also for the binding energies of three non-strange baryon systems. We make emphasis on observable effects related to quark antisymmetry and its interplay with quark dynamics.