586 research outputs found

    Exclusive Charmless BB Decays in QCD

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    The problem of hadronic input in charmless nonleptonic B decays is discussed. QCD sum rules and their light-cone versions (LCSR) provide an important part of this input, such as the decay constant fBf_B and BπB\to \pi form factor. Employing the LCSR technique, the BππB\to \pi\pi hadronic matrix elements with emission, penguin and annihilation topologies are calculated, with no evidence for large nonfactorizable effects and/or strong phases.Comment: 6 pages, Invited talk at the First Workshop on Theory, Phenomenology and Experiments in Heavy Flavour Physics, Anacapri, Italy, May 29-31 200

    Quantum Chromodynamics and Hadrons: an Elementary Introduction

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    Notes of five lectures given at the 2003 European School of High-Energy Physics, Tsakhkadzor, Armenia, September 2003Comment: 52 pages, 25 figures, latex, cernrep.cls; lectures at the 2003 European School of High-Energy Physics, Tsakhkadzor, Armenia, September 200

    BππB \to \pi\pi Decay in QCD

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    A new method is suggested to calculate the BππB\to \pi\pi hadronic matrix elements from QCD light-cone sum rules. To leading order in αs\alpha_s and 1/mb1/m_b, the sum rule reproduces a factorizable matrix element, in accordance with the prediction of the QCD factorization approach. Whereas the QCD factorization can only take into account the nonfactorizable corrections induced by hard-gluon exchanges, the method suggested here also allows a systematic inclusion of soft-gluon effects. In this paper, I concentrate on the latter aspect and present a calculation of the nonfactorizable soft-gluon exchange contributions to BππB\to \pi\pi. The result, including twist 3 and 4 terms, is suppressed by one power of 1/mb1/m_b with respect to the factorizable amplitude. Despite its numerical smallness, the soft effect is at the same level as the O(αs)O(\alpha_s) correction to the QCD factorization formula for BππB\to \pi\pi. The method suggested here can be applied to matrix elements of different topologies and operators and to various other B-decay channels. I also comment on the earlier applications of QCD sum rules to nonleptonic decays of heavy mesons.Comment: 20 pages, 2 figures, Latex, epsfig.sty, a few sentences reworded, two comments added, version to appear in Nucl. Phys.

    Applications of QCD Sum Rules to Heavy Quark Physics

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    In these lectures, I present several important applications of QCD sum rules to the decay processes involving heavy-flavour hadrons. The first lecture is introductory. As a study case, the sum rules for decay constants of the heavy-light mesons are considered. They are relevant for the leptonic decays of BB-mesons. In the second lecture I describe the method of QCD light-cone sum rules used to calculate the heavy-to-light form factors at large hadronic recoil, such as the BπνB\to \pi \ell \nu_\ell form factors. In the third lecture, the nonlocal hadronic amplitudes in the flavour-changing neutral current decays BK()B\to K^{(*)}\ell\ell are discussed. Light-cone sum rules provide important nonfactorizable contributions to these amplitudes.Comment: Lectures at the Helmholtz International Summer School "Physics of Heavy Quarks and Hadrons'', July 2013, Dubna, Russia. SI-HEP-2013-1

    Counting contact terms in BVγB\to V\gamma decays

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    We clarify the origin and cancellation of contact terms in the weak annihilation amplitudes contributing to BVγB\to V \gamma. It is demonstrated that the photon emission from the final-state quarks vanishes in the chiral limit of massless quarks. The contact terms in the QCD light-cone sum rule evaluation of the weak annihilation amplitudes are also discussed.Comment: 16 pages, 2 figures, Latex, ws-p8-50x6-00.cls, to be published in Sergei Matinian Festschrift ``From Integrable Models to Gauge Theories.'', Eds. V. Gurzadyan, A. Sedrakyan, World Scientific, 200

    Form factors in BππνˉB\to \pi\pi\ell\bar\nu_\ell from QCD light-cone sum rules

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    The form factors of the semileptonic BππνˉB\to \pi\pi\ell\bar\nu decay are calculated from QCD light-cone sum rules with the distribution amplitudes of dipion states. This method is valid in the kinematical region, where the hadronic dipion state has a small invariant mass and simultaneously a large recoil. The derivation of the sum rules is complicated by the presence of an additional variable related to the angle between the two pions. In particular, we realize that not all invariant amplitudes in the underlying correlation function can be used, some of them generating kinematical singularities in the dispersion relation. The two sum rules that are free from these ambiguities are obtained in the leading twist-2 approximation, predicting the Bˉ0π+π0\bar{B}^0\to \pi^+\pi^0 form factors FF_{\perp} and FF_{\parallel} of the vector and axial bub\to u current, respectively. We calculate these form factors at the momentum transfers 0<q2120<q^2\lesssim 12 GeV2^2 and at the dipion mass close to the threshold 4mπ24m_\pi^2. The sum rule results indicate that the contributions of the higher partial waves to the form factors are suppressed with respect to the lowest PP-wave contribution and that the latter is not completely saturated by the ρ\rho-meson term.Comment: 17 pages, 4 figures, a few comments and references added, version to be published in Nucl.Phys.

    QCD Sum Rules, a Modern Perspective

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    An introduction to the method of QCD sum rules is given for those who want to learn how to use this method. Furthermore, we discuss various applications of sum rules, from the determination of quark masses to the calculation of hadronic form factors and structure functions. Finally, we explain the idea of the light-cone sum rules and outline the recent development of this approach.Comment: 84 pages, 14 figures, Latex,epsfig,sprocl.sty. To be published in the Boris Ioffe Festschrift ''At the Frontier of Particle Physics / Handbook of QCD'', edited by M. Shifman (World Scientific, Singapore, 2001)
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