X(1576) as Diquark-Antidiquark Bound State

We propose that the broad $1^{--}$ resonance structure recently discovered by BES in $J/\psi\to K^{+}K^{-}\pi^{0}$ is the P-wave excitation of a diquark-antidiquark bound state. This interpretation implies that there exists a negative parity, vector nonet. A rough estimate of the mass spectrum of the nonet is presented, and the prediction for the mass of X(1576) is consistent with the experimental data. The OZI allowed strong decays are studied, it can decay into two pseudoscalars or one pseudoscalar plus one vector meson. A crucial prediction is that X(1576) should dominantly decay into $K^{+}K^{-}$, $K_{L}K_{S}$, $\phi\pi^{0}$. Since the isospin of X(1576) is $\mathbf{1}$, the observation of $I_3=1$ or $I_3=-1$ states which predominantly decays into strange mesons could provide another important test to our proposal. To search the charged $I_3=1$ isospin partner associated with X(1576) in $J/\psi\to \eta\pi^{+}\pi^{-}$, $J/\psi\to K^{+}K_{L}\pi^{-}$, $J/\psi\to K^{+}K_{S}\pi^{-}$, $J/\psi\to \phi\pi^{+}\pi^{-}$ is suggested.Comment: 15 pages, 1 figur

Chromomagnetism, flavour symmetry breaking and S-wave tetraquarks

The chromomagnetic interaction, with full account for flavour-symmetry breaking, is applied to S-wave configurations containing two quarks and two antiquarks. Phenomenological implications are discussed for light, charmed, charmed and strange, hidden-charm and double-charm mesons, and extended to their analogues with beauty.Comment: 16 pages, 2 figures, RevTeX, Refs. updated, further typos corrected, to appear in EPJ

Isovector and hidden-beauty partners of the X(3872)

The isovector partners of the X(3872), recently found at BES III, Belle and CLEO-c were predicted in a simple model based on the chromomagnetic interaction among quarks (H. Hogaasen, J-M. Richard and P. Sorba, Phys. Rev. D73, 054013, 2006). The extension to the hidden-beauty sector is discussed.Comment: Some references added. More details on the width and decay modes. To appear in Phys. Lett.

Grozdovi obojenih s-valnih kvarkova s lomljenjem okusne simetrije

We study the properties of coloured three-particle s-wave quark clusters when flavour symmetry is broken. The relevance of such clusters for models of pentaquarks is shortly mentioned.Proučavamo svojstva obojenih tročestičnih s-valnih kvarkovskih grozdova s lomljenjem okusne simetrije. Kratko se spominje važnost tih grozdova za pentakvarkovske modele

Diquarks and antiquarks in exotics: a menage a trois and a menage a quatre

A menage a trois is very different from an ordinary family. Similarly, exotic hadrons with both qq and qbar q pairs have important color-space correlations that are completely absent in ordinary mesons and baryons. The presence of both types of pairs requires attention to the basic QCD physics that the q qbar interaction is much stronger than the qq interaction. This new physics in multiquark systems produces color structures totally different from those of normal hadrons, for example the ud system is utterly unlike the ud diquark in the uds Lambda baryon. The color-space correlations produce unusual experimental properties in tetraquarks with heavy quark pairs which may be relevant for newly discovered mesons like the X(3872) resonance. Tetraquark masses can be below the two-meson threshold for sufficiently high quark masses. A simple model calculation shows the b q bbar ubar and b q cbar qbar tetraquarks below the B Bbar and B Dbar thresholds. Some of these states have exotic electric charge and their decays might have striking signatures involving monoenergetic photons and/or pions.Comment: Journal version (PLB

Spectrum of the Y=2 Pentaquarks

By assuming a mass formula for the spectrum of the Y=2 pentaquarks, where the chromo-magnetic interaction plays a main role, and identifying the lightest state with the Theta^+(1540), we predict a spectrum in good agreement with the few I=0 and I=1 candidates proposed in the past.Comment: 12 pages, 4 figures, LaTe

The discovery and properties of pentaquarks

The pentaquarks are exotic baryons formed of four quarks and an antiquarks. Their existence has been discussed in the literature over the last 30 years or more, first in connection with kaon nucleon scattering data. The subject has been revived by the end of 2002 when experimental evidence of a narrow baryon of strangeness $S$ = + 1, and mass $M \simeq$ 1530 MeV has been found. This is interpreted as the lightest member of an SU(3)-flavor antidecuplet. Here we shall mainly review the predictions of pentaquark properties as e.g. mass, spin and parity, within constituent quark models. Both light and heavy pentaquarks will be presented.Comment: Plenary talk, MESON2004 Conference Proceedings, Crakow, June 4-8 200