144 research outputs found

    Decays rates for S- and P-wave bottomonium

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    We use the Bodwin-Braaten-Lepage factorization scheme to separate the long- and short-distance factors that contribute to the decay rates of Υ\Upsilon, ηb\eta_b (S-wave) and χb\chi_b,hbh_b (P-wave). The long distance matrix elements are calculated on the lattice in the quenched approximation using a non-relativistic formulation of the bb quark dynamics.Comment: 3 pages Latex using espcrc2.sty and epsf.sty + 2 postscript figure

    Prompt J/psi Polarization at the Tevatron

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    The polarization of prompt J/psi at the Tevatron is calculated within the nonrelativistic QCD (NRQCD) factorization framework. The contribution from radiative decays of P-wave charmonium states decreases, but does not eliminate, the transverse polarization at large transverse momentum. The prediction agrees with measurements from the CDF collaboration at intermediate values of p_T, but disagrees at the large values of p_T measured.Comment: 5 pages, 2 figures, Talk given at 5th Workshop on QCD, 3-7 January 2000, Villefranche-sur-Mer, Franc

    Resummation of QCD Corrections to the eta_c Decay Rate

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    We examine the ratio of the decay rate of the eta_c into light hadrons to the decay rate into photons and find that most of the large next-to-leading-order (NLO) correction is associated with running of the strong coupling alpha_s. We resum such contributions by analyzing final-state chains of vacuum-polarization bubbles. We show that the nonperturbative parts of the bubble chains can be absorbed into a color-octet matrix element, once one has used contour deformations of the phase-space integrals to cancel certain contributions. We argue that these contributions are incompatible with the uncertainty principle. We also argue that perturbation theory is reliable only if one carries out the phase-space integrations before the perturbation summation. Our results are in good agreement with experiment and differ considerably from those that one obtains by applying the scale-setting method of Brodsky, Lepage, and Mackenzie to the NLO result.Comment: 41 pages, REVTEX, corrected minor typos in tex

    χQJ+\chi_{QJ} \to\ell^+\ell^- within and beyond the Standard Model

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    We revisit χQJ+\chi_{QJ}\to \ell^+\ell^- (with J=0,1,2J=0,1,2 and Q=b,cQ=b,c) within the Standard Model (SM). The electro-magnetic contributions are given in color-singlet model with non-vanishing lepton masses at the leading order of vv. Numerically, the branching ratios of χQJ+\chi_{QJ}\to\ell^{+}\ell^{-} predicted within the SM are so small that such decays are barely possible to be detected at future BESIII and SuperB experiments, but may be possible to be observed at the LHC. We investigate χb0+\chi_{b0}\to\ell^+\ell^- in Type-II 2HDM with large tanβ\tan\beta, and χb2+\chi_{b2}\to\ell^+\ell^- in the Randall-Sundrum model, to see their chance to be observed in future experiments.Comment: 11 pages, 8 figures. To match the published versio

    Υ\Upsilon radiative decays to light quark jets and color octet mechanism

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    We study radiative decays of Υ\Upsilon to light quark jets in nonrelativistic QCD by taking both the color singlet and color octet bbˉb\bar b operators into consideration. The cut for quark jet energy and cut for the angle between two quark jets are introduced. The sensitivity to the soft and collinear singularities in the loop integrals are greatly reduced by these cuts. With the jet energy cut of about 1 GeV, and the jet angle cut of about 3636^\circ, the branching ratio for Υγqqˉ\Upsilon\to\gamma q\bar q is found to be 8.2×1048.2\times 10^{-4} from color singlet contributions. The color octet contributions could be much larger than that of color singlet, depending on the estimate of the color octet matrix elements. This process may provide a new test for the color octet mechanism in nonrelativistic QCD.Comment: journal version; a few references adde

    Fragmentation Function in Non-Equilibrium QCD Using Closed-Time Path Integral Formalism

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    In this paper we implement Schwinger-Keldysh closed-time path integral formalism in non-equilibrium QCD to the definition of Collins-Soper fragmentation function. We consider a high p_T parton in QCD medium at initial time t_0 with arbitrary non-equilibrium (non-isotropic) distribution function f(\vec{p}) fragmenting to hadron. We formulate parton to hadron fragmentation function in non-equilibrium QCD in the light-cone quantization formalism. It may be possible to include final state interactions with the medium via modification of the Wilson lines in this definition of the non-equilibrium fragmentation function. This may be relevant to study hadron production from quark-gluon plasma at RHIC and LHC.Comment: 15 pages latex, Accepted for Publication in European Physical Journal

    Inclusive SS-wave charmonium productions in BB decays

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    The inclusive SS-wave charmonium production rates in BB decays are considered using the Bodwin-Braaten-Lepage (BBL) approach, including the relativistic corrections and the color-octet mechanism suggested as a possible solution to the ψ\psi^{'} puzzle at the Tevatron. We first consider relativistic and radiative corrections to J/ψe+eJ/\psi \rightarrow e^{+} e^{-} and J/ψJ/\psi \rightarrow Light Hadrons (LH), in order to determine two nonperturbative parameters, J/ψO1(3S1)J/ψ\langle J/\psi | O_{1} (^{3}S_{1}) | J/\psi \rangle, J/ψP1(3S1)J/ψ\langle J/\psi | P_{1} (^{3}S_{1}) | J/\psi \rangle, in the factorization formulae for these decays. Using these two matrix elements and including the color-octet ccˉ(3S1)c\bar{c}(^{3}S_{1}) state contribution, we get a moderate increase in the decay rates for BB decays into J/ψ (or ψ) +XJ/\psi ~({\rm or}~\psi^{'}) ~+ X. Our results, B(BJ/ψ (or ψ)+X)=0.58 (0.23)%B(B \rightarrow J/\psi~({\rm or}~\psi^{'}) + X) = 0.58~(0.23) \% for Mb=5.3M_{b} = 5.3 GeV, get closer to the recent CLEO data. As a byproduct, we prefer a larger decay rate for ηc\eta_{c} \rightarrow LH compared to the present data.Comment: 12 page

    Power counting and effective field theory for charmonium

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    We hypothesize that the correct power counting for charmonia is in the parameter Lambda_QCD/m_c, but is not based purely on dimensional analysis (as is HQET). This power counting leads to predictions which differ from those resulting from the usual velocity power counting rules of NRQCD. In particular, we show that while Lambda_QCD/m_c power counting preserves the empirically verified predictions of spin symmetry in decays, it also leads to new predictions which include: A hierarchy between spin singlet and triplet octet matrix elements in the J/psi system. A quenching of the net polarization in production at large transverse momentum. No end point enhancement in radiative decays. We discuss explicit tests which can differentiate between the traditional and new theories of NRQCD.Comment: 18 pages, 1 figure Replaced plot of the psi polarization parameter alpha as a function of transverse momentum. Alpha is now closer to zero for large transverse moment

    Fragmentation Functions for Lepton Pairs

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    We calculate the fragmentation function for a light quark to decay into a lepton pair to leading order in the QCD coupling constant. In the formal definition of the fragmentation function, a QED phase must be included in the eikonal factor to guarantee QED gauge invariance. We find that the longitudinal polarization fraction is a decreasing function of the factorization scale, in accord with the intuitive expectation that the virtual photon should behave more and more like a real photon as the transverse momomentum of the fragmenting quark increases.Comment: 13 pages, 4 figures, normalization corrected, text abbreviate

    Resumming the color-octet contribution to e+ e- -> J/psi + X

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    Recent observations of the spectrum of J/psi produced in e+ e- collisions at the Upsilon(4S) resonance are in conflict with fixed-order calculations using the Non-Relativistic QCD (NRQCD) effective field theory. One problem is that leading order color-octet mechanisms predict an enhancement of the cross section for J/psi with maximal energy that is not observed in the data. However, in this region of phase space large perturbative corrections (Sudakov logarithms) as well as enhanced nonperturbative effects are important. In this paper we use the newly developed Soft-Collinear Effective Theory (SCET) to systematically include these effects. We find that these corrections significantly broaden the color-octet contribution to the J/psi spectrum. Our calculation employs a one-stage renormalization group evolution rather than the two-stage evolution used in previous SCET calculations. We give a simple argument for why the two methods yield identical results to lowest order in the SCET power counting.Comment: 27 pages, 7 figure
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