4,671 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

    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

    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

    Pionic transitions from X(3872) to chi_{cJ}

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    We consider transitions from the resonance X(3872) to the chi_{cJ} states of charmonium with emission of one or two pions as a means of studying the structure of the X resonance. We find that the relative rates for these transitions to the final states with different J significantly depend on whether the initial state is a pure charmonium state or a four-quark/molecular state.Comment: 12 page

    Bottomonium dipion transitions

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    Dipion transitions of the subthreshold bottomonium levels Υ(nS)Υ(nS)ππ\Upsilon (nS)\to \Upsilon (n'S) \pi\pi with n>n,n=2,3,4,n=1,2n>n', n=2,3,4, n'=1,2 are studied in the framework of the chiral decay Lagrangian, derived earlier. The channels BBˉ,BBˉ+c.c,BBˉB\bar B, B\bar B^*+ c.c, B^* \bar B^* are considered in the intermediate state and realistic wave functions of Υ(nS),B\Upsilon (n S),B and BB^* are used in the overlap matrix elements. Imposing the Adler zero requirement on the transition matrix element, one obtains 2d and 1d dipion spectra in reasonable agreement with experiment.Comment: 34 pages, 18 figure

    Soliton-antisoliton pair production in particle collisions

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    We propose general semiclassical method for computing the probability of soliton-antisoliton pair production in particle collisions. The method is illustrated by explicit numerical calculations in (1+1)-dimensional scalar field model. We find that the probability of the process is suppressed by an exponentially small factor which is almost constant at high energies.Comment: 4 pages, 3 figures, journal versio

    Decays of b hadrons and a possible new four-quark interaction

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    A possibility is considered of explaining the low experimental value of the ratio of the lifetimes tau(Lambda_b)/tau(B_d) by a new `centiweak' four-quark interaction, i.e with a strength on the order of 10^{-2}G_F. It is noted that the considered interaction can also improve agreement with the data on low semileptonic branching ratio B_{sl}(B) in B meson decays with a simultaneous slight decrease in the prediction for the average charm yield in those decays. The proposed new interaction modifies within the present experimental limits the predictions for differences of lifetimes among B mesons, and can thus be probed by more precise data on these differences. A sample model is briefly discussed, where the new interaction arises through a weak SU(2) singlet scalar field with quantum numbers of a diquark.Comment: 10 page
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