207 research outputs found

    Are there compact heavy four-quark bound states?

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    We present an exact method to study four-quark systems based on the hyperspherical harmonics formalism. We apply it to several physical systems of interest containing two heavy and two light quarks using different quark-quark potentials. Our conclusions mark the boundaries for the possible existence of compact, non-molecular, four-quark bound states. While QQnˉnˉQQ\bar n \bar n states may be stable in nature, the stability of QQˉnnˉQ\bar Qn \bar n states would imply the existence of quark correlations not taken into account by simple quark dynamical modelsComment: 10 pages, 1 figure. Accepted for publication in Phys. Rev.

    Mass and width of the dd' resonance in nuclei

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    We calculated the mass and width of the dd' resonance inside nuclei within a nucleon-Δ\Delta model by including the self-energy of the Δ\Delta in the NΔN\Delta propagator. We found that in the nuclear medium the width of the dd' is increased by one order of magnitude while its mass changes only by a few MeV. This broadening of the width of the dd' resonance embedded in nuclei is consistent with the experimental observations so that the dd' can be understood as a NΔN\Delta resonance. Thus, given the freedom between either isospin 0 or isospin 2 for the dd', our results give weigth to the isospin-2 assignment.Comment: 14 pages, RevteX type, 2 eps figures. To be published in Phys. Rev. C (September

    Open-charm meson spectroscopy

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    We present a theoretical framework that accounts for the new DJD_J and DsJD_{sJ} mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional PP-wave quark-antiquark states and four-quark components. The narrowest states are basically PP-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.Comment: 15 pages, 5 tables. Accepted for publication in Phys. Rev.

    Does the quark cluster model predict any isospin two dibaryon resonance?

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    We analyze the possible existence of a resonance in the JP=0J^P=0^- channel with isospin two by means of nucleon-Δ\Delta interactions based on the constituent quark model. We solve the bound state and the scattering problem using two different potentials, a local and a non-local one. The non-local potential results to be the more attractive, although not enough to generate the experimentally predicted resonance.Comment: 9 pages in Latex (revtex), 2 eps figures available under reques

    Four-quark spectroscopy within the hyperspherical formalism

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    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 NN-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+0^{+-} and non-exotic 2++2^{++} quantum numbers may be bound independently of the mass of the quark. 2+2^{+-} and 1+1^{+-} states become attractive only for larger mass of the quarks.Comment: 20 pages, 3 figure

    Nature of the light scalar mesons

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    Despite the apparent simplicity of meson spectroscopy, light scalar mesons cannot be accommodated in the usual qqˉq\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 qqˉq\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.Comment: 14 pages, 1 figure, accepted for publication in Phys. Rev.

    Long- and medium-range components of the nuclear force in quark-model based calculations

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    Quark-model descriptions of the nucleon-nucleon interaction contain two main ingredients, a quark-exchange mechanism for the short-range repulsion and meson-exchanges for the medium- and long-range parts of the interaction. We point out the special role played by higher partial waves, and in particular the 1F3, as a very sensitive probe for the meson-exchange part employed in these interaction models. In particular, we show that the presently available models fail to provide a reasonable description of higher partial waves and indicate the reasons for this shortcoming.Comment: 19 pages, 7 figure

    Deuteron NN*(1440) components from a chiral quark model

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    We present a nonrelativistic coupled-channel calculation of the deuteron structure including Delta Delta and NN^*(1440) channels, besides the standard NN S and D-wave components. All the necessary building blocks to perform the calculation have been obtained from the same underlying quark model. The calculated NN^*(1440) probabilities find support in the explanation given to different deuteron reactions.Comment: 4 pages; revtex4, Accepted for publication in Phys. Rev. C (Brief Report

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

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    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 QQnˉnˉQQ\bar n \bar n states may be stable in nature, the stability of QQˉnnˉQ\bar Qn \bar n states would imply the existence of quark correlations not taken into account by simple quark dynamical models.Comment: 3 pages. Contribution to the 20th European Conference on Few-Body Problems in Physics, Pisa, Italy. To be published in Few-Body system
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