12,114 research outputs found

    QCD Sum Rule Analysis of the Subleading Isgur-Wise Form Factor χ2(vv)\chi_2(v\cdot v')

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    We present a QCD sum rule calculation of the spin-symmetry violating universal function χ2(vv)\chi_2(v\cdot v'), which appears at order 1/mQ1/m_Q in the heavy quark expansion of meson form factors. This function vanishes in the standard approximation, where radiative effects are neglected. For the first time, the complete set of diagrams arising at order αs\alpha_s is evaluated. In particular, we find χ2(1)=(3.8±0.4)%\chi_2(1) = -(3.8\pm 0.4)\% at zero recoil, indicating that 1/mQ1/m_Q corrections induced by the chromo-magnetic moment operator are small.Comment: (10 pages, REVTEX, 2 figures not included) SLAC-PUB-5915, WIS-92/70/Sep-P

    Two-Loop Renormalization of Heavy--Light Currents at Order 1/m_Q in the Heavy-Quark Expansion

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    We present exact results, at next-to-leading order in renormalization-group improved perturbation theory, for the Wilson coefficients appearing at order 1/m_Q in the heavy-quark expansion of heavy-light current operators. To this end, we complete the calculation of the corresponding two-loop anomalous dimension matrix. Our results are important for determinations of |V_{ub}| using exclusive and inclusive semileptonic B decays. They are also relevant to computations of the decay constant f_B based on a heavy-quark expansion.Comment: 16 pages, 2 figures; third author added and one reference updated, results unchange

    Impact of Four-Quark Shape Functions on Inclusive B Decay Spectra

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    It has recently been pointed out that a new class of subleading shape functions involving B-meson matrix elements of non-local four-quark operators contributes at order Lambda_{QCD}/m_b to B->X_u+l+nu decay distributions in the endpoint region. The corresponding functions f_u(omega) and f_v(omega) are estimated using the vacuum-insertion approximation. A numerical analysis of various B->X_u+l+nu decay spectra suggests that these power corrections are very small, below present theoretical uncertainties due to other subleading shape-function contributions.Comment: 8 pages, 2 figures; minor revisions and figure added; version to appear in Eur. Phys. J.

    Form Factor Relations for Heavy-to-Light Transitions

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    Assuming simple properties of the spectator particle in weak decays the form factors of hadronic current matrix elements are shown to be related to a single universal function. The Isgur-Wise result for heavy-to-heavy transitions follows as well as similar relations for heavy-to-light decay processes. The approximation should hold for total energies of the final particle large compared to the confinement scale. A comparison with experimentally determined D-decay form factors and QCD sum rule results for B-decays is very encouraging.Comment: 12 pages, Latex; Relativistic covariant form, results unchanged, references added, to be published in Physics Lett.

    Effective Field Theory and Heavy Quark Physics

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    These notes are based on five lectures presented at the 2004 Theoretical Advanced Study Institute (TASI) on ``Physics in D>=4''. After a brief motivation of flavor physics, they provide a pedagogical introduction to effective field theory, the effective weak Lagrangian, and the technology of renormalization-group improved perturbation theory. These general methods are then applied in the context of heavy-quarks physics, introducing the concepts of heavy-quark and soft-collinear effective theory.Comment: Lectures presented at TASI 2004 (39 pages

    QCD Sum-Rule Calculation of the Kinetic Energy and Chromo-Interaction of Heavy Quarks Inside Mesons

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    We present a QCD sum-rule determination of the heavy-quark kinetic energy inside a heavy meson, λ1/2mQ-\lambda_1/2 m_Q, which is consistent with the field-theory analog of the virial theorem. We obtain -\lambda_1\approx (0.10\pm 0.05)~\mbox{GeV}^2, significantly smaller than a previous sum-rule result, but in good agreement with recent determinations from the analysis of inclusive decays. We also present a new determination of the chromo-magnetic interaction, yielding \lambda_2(m_b)=(0.15\pm 0.03)~\mbox{GeV}^2. This implies m_{B^*}^2-m_B^2=(0.60\pm 0.12)~\mbox{GeV}^2, in good agreement with experiment. As a by-product of our analysis, we derive the QCD sum rules for the three form factors describing the meson matrix element of a velocity-changing current operator containing the gluon field-strength tensor.Comment: 13 pages LaTeX (A4), 3 figure

    Uncertainties in the Determination of Vcb|V_{cb}|

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    I discuss the theoretical uncertainties in the extraction of Vcb|\,V_{cb}| from semilep\-to\-nic decays of BB mesons, taking into account the most recent theoretical developments. The main sources of uncertainty are identified both for the exclusive decay mode BDνˉB\to D^*\ell\,\bar\nu and for the inclusive channel BXνˉB\to X\,\ell\,\bar\nu. From an analysis of the available experimental data, I obtain Vcbexcl=0.041±0.003exp±0.002th|\,V_{cb}|_{\rm excl} = 0.041\pm 0.003_{\rm exp}\pm 0.002_{\rm th} from the exclusive mode, and Vcbincl=0.040±0.001exp±0.005th|\,V_{cb}|_{\rm incl} = 0.040\pm 0.001_{\rm exp}\pm 0.005_{\rm th} from the inclusive mode. I also give a prediction for the slope of the form factor F(w){\cal{F}}(w) at zero recoil, which is ϱ^2=0.8±0.3\widehat\varrho^2=0.8\pm 0.3.Comment: Proceedings of 1995 Moriond Conference on Electroweak Interactions and Unified Theories, 11 pages, 3 figures available as uu-encoded postscript file
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