7,340 research outputs found

    The cˉc{\bar c} c purity of ψ(3770)\psi(3770) and ψ\psi' challenged

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    It is suggested that the resonance ψ(3770)\psi(3770) may contain a sizeable (O(10O(10%) in terms of the probability weight factor) four-quark component with the up- and down- quarks and antiquarks in addition to the ccˉc {\bar c} pair, which component in itself has a substantial part with the isospin I=1. Furthermore such four-quark part of the wave function should also affect the properties of the ψ\psi' charmonium resonance through the ψ(3770)ψ\psi(3770) - \psi' mixing previously considered in the literature. It is argued that an admixture of extra light quark pairs can explain a possible discrepancy between the theoretical expectations and the recent data on the non-DDˉD {\bar D} decay width of the ψ(3770)\psi(3770) and the ratio of the yield of charged and neutral DD meson pairs in its decays, as well as on the extra rate of the ψ\psi' direct decay into light hadrons and the rate of the decay ψπ0J/ψ\psi' \to \pi^0 J/\psi. It is further argued that the suggested four-quark component of the wave function of the ψ(3770)\psi(3770) should give rise to a measurable rate of the decays ψ(3770)ηJ/ψ\psi(3770) \to \eta J/\psi and ψ(3770)π0J/ψ\psi(3770) \to \pi^0 J/\psi.Comment: 13 page

    Heavy quark spin symmetry breaking in near-threshold JPC=1J^{PC}=1^{--} quarkonium-like resonances

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    A mixing of near-threshold quarkonium-like resonances with heavy meson-antimeson pairs results in an enhancement of heavy quark spin symmetry breaking, since the meson pairs are not eigenstates of the heavy quark spin. The decomposition of PP-wave states of meson pairs in terms of the heavy-quark-pair spin states is considered in the channel with JPC=1J^{PC}=1^{--}, which is directly produced in e+ee^+e^- annihilation. Specific processes are suggested for experimental study of the effects of the mixing with heavy meson pairs and of the internal spin structure of bottomonium and charmonium resonances.Comment: 15 page

    Anisotropic flow of identified particles in Au+Au collisions at AGS energy

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    Anisotropic flow of protons, π±\pi^{\pm}, K+K^+, deuterons, tritons, 3^3He, and 4^4He is analyzed as a function of transverse momentum for different centralities of the collision.Comment: RevTex, 4 pages, 4 figures included as eps files. To be published in the Proceedings of QM97, Tsukuba, Japa

    Ultra-relativistic nuclear collisions: event shape engineering

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    The evolution of the system created in a high energy nuclear collision is very sensitive to the fluctuations in the initial geometry of the system. In this letter we show how one can utilize these large fluctuations to select events corresponding to a specific initial shape. Such an "event shape engineering" opens many new possibilities in quantitative test of the theory of high energy nuclear collisions and understanding the properties of high density hot QCD matter.Comment: 6 pages, 5 figure

    Semiclassical Calculation of Photon-Stimulated Schwinger Pair Creation

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    We consider the electron-positron pair creation by a photon in an external constant electric field. The presented treatment is based on a purely quasiclassical calculation of the imaginary part of the on-shell photon polarization operator. By using this approach we find the pair production rate for photons with polarization parallel as well as orthogonal to the external electric field in the leading order in the parameter eE/m2eE / m ^ 2, which has been recently found by other methods. For the orthogonal polarization we also find a new contribution to the rate, which is leading in the ratio of the photon energy to the electron mass ω/m\omega/m. We also reproduce by a purely geometrical calculation the exponential factor in the probability of the stimulated pair creation at arbitrary energy of the photon.Comment: 16 pages, 4 figure

    Anisotropic collective phenomena in ultra-relativistic nuclear collisions

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    For a detailed review of this subject I refer to a recent paper \cite{Voloshin:2008dg}; in this talk I only very briefly comment on a few most important questions: (a) Very recent significant progress in viscous hydrodynamics calculations (b) Initial eccentricity/flow fluctuations, the effect of which has been clarified recently (c) Initial conditions, in particular the role of the gradients in the initial velocity field, (d) Puzzling system size dependence of directed flow (e) Azimuthal correlations that are sensitive to the strong parity violation (f) Future measurements at RHIC and LHC, including pp-collisionsComment: 6 pages. Proceedings. Invited talk at PANIC 2008 conference, Eilat, Israel, November 200

    Experimental study of local strong parity violation in relativistic nuclear collisions

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    Parity-odd domains, corresponding to non-trivial topological solutions of the QCD vacuum, might be created in relativistic heavy ions collisions. These domains are predicted to lead to charge separation along the system orbital momentum of the system created in non-central collisions. Three-particle mixed harmonics azimuthal correlator is a \P even observable but directly sensitive to the charge separation effect. Using this observable to analyze Au+Au and Cu+Cu collisions at sNN=200\sqrt{s_{NN}}=200 and 62 GeV, STAR detects a signal consistent with several of the theoretical expectations. Possible contributions from effects not related to parity violation are studied with existing event generators, which fail to describe the data. Future directions in studying the effect are discussed.Comment: Proceedings, plenary invited talk at Quark Matter 2009 Conference, Knoxville, Tennessee. One reference added. Final versio

    Bound States of the Heavy Flavor Vector Mesons and Y(4008) and Z1+(4050)Z^{+}_1(4050)

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    The DDˉD^{*}\bar{D}^{*} and BBˉB^{*}\bar{B}^{*} systems are studied dynamically in the one boson exchange model, where π\pi, η\eta, σ\sigma, ρ\rho and ω\omega exchanges are taken into account. Ten allowed states with low spin parity are considered. We suggest that the 11^{--}, 2++2^{++}, 0++0^{++} and 0+0^{-+} BBˉB^{*}\bar{B}^{*} molecules should exist, and the DDˉD^{*}\bar{D}^{*} bound states with the same quantum numbers very likely exist as well. However, the CP exotic (1+1^{-+}, 2+2^{+-}) BBˉB^{*}\bar{B}^{*} and DDˉD^{*}\bar{D}^{*} states may not be bound by the one boson exchange potential. We find that the I=0 configuration is more deeply bound than the I=1 configuration, hence Z1+(4050)Z^{+}_1(4050) may not be a DDˉD^{*}\bar{D}^{*} molecule. Although Y(4008) is close to the DDˉD^{*}\bar{D}^{*} threshold, the interpretation of Y(4008) as a DDˉD^{*}\bar{D}^{*} molecule is not favored by its huge width. 11^{--} DDˉD^{*}\bar{D}^{*} and BBˉB^{*}\bar{B}^{*} states can be produced copiously in e+ee^{+}e^{-} annihilation, detailed scanning of the e+ee^{+}e^{-} annihilation data near the DDˉD^{*}\bar{D}^{*} and BBˉB^{*}\bar{B}^{*} threshold is an important check to our predictions.Comment: 17 pages,6 figur

    Comment on "Summing One-Loop Graphs at Multi-Particle Threshold"

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    The propagator of a virtual ϕ\phi-field with emission of nn on-mass-shell particles all being exactly at rest is calculated at the tree-level in λϕ4\lambda \phi^4 theory by directly solving recursion equations for the sum of Feynman graphs. It is shown that the generating function for these propagators is equivalent to a Fourier transform of the recently found Green's function within the background-field technique for summing graphs at threshold suggested by Lowell Brown. Also the derivation of the result that the tree-level on-mass-shell scattering amplitudes of the processes 2n2 \to n are exactly vanishing at threshold for n>4n > 4 is thus given in the more conventional Feynman diagram technique.Comment: 7 pages, LaTeX, TPI-MINN-92/46-

    Non-factorizable terms, heavy quark masses, and semileptonic decays of D and B mesons

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    The non-factorizable terms in the operator product expansion have been recognized as one of theoretical obstacles for precision determination of the mixing parameter VubV_{ub} from semileptonic B decays. It is pointed out here that the recent CLEO data on the parameters of the heavy quark expansion λ1\lambda_1 and Λˉ{\bar \Lambda}, combined with a theoretical bound on λ1\lambda_1 strongly favor the existence of a sizeable contribution of non-factorizable terms in semileptonic decays of DD mesons. Thus these terms are likely to solve the long-standing problem of the deficit of semileptonic decay rate of the DD mesons, and with better data their magnitude can be determined and used in studies of the parameter VubV_{ub}.Comment: 7 pages, 1 figur