Form factors of

Khodjamirian, Alexander

doi:10.1007/s100520050357

Cited by 130 publications

(349 citation statements)

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“…Thus, our analysis does not confirm the opposite conclusions drawn in [17] which uses the same calculational scheme, but a larger value of the auxiliary Borel parameter M 2 , notably 1.5 GeV 2 , instead of values M 2 < 1 GeV 2 as in our approach, (which follows [12]) and more coefficients in the conformal expansion of the pion DA.…”

Section: Two-photon Processes For π 0 and η(η ′ ) In Qcdcontrasting

confidence: 83%

Pion-Photon Transition Form Factor and Pion Distribution Amplitude in QCD: Facing the Enigmatic Behavior of the BaBar Data

Stefanis

Bakulev²,

Михайлов³

et al. 2012

Nuclear Physics B - Proceedings Supplements

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We present an extended analysis of the data for the pion-photon transition form factor from different experiments, CELLO, CLEO, and BaBar, and discuss various theoretical approaches which try to reason from them. We focus on the divergent behavior of the BaBar data for the pion and those for the η(η ′ ) pseudoscalar mesons and comment on recently proposed explanations for this discrepancy. We argue that it is not possible at present to accommodate these data within the standard QCD framework self-consistently. Keywords:Meson transition form factors, pion distribution amplitude, QCD (light-cone) sum rules 1. Two-photon processes for π 0 and η(η ′ ) in QCD At the basis of applications of Quantum Chromodynamics (QCD), which governs the interactions of quarks and gluons, is the property of factorization of corresponding amplitudes in hard processes. Proving the property of factorization means that a hadronic process at large momentum transfer can be dissected in a product of distinct quantities each associated with separate regimes of dynamics. Then, subprocesses developing at short distances and involving partons-quarks and gluons-can be accurately described in a systematic way within perturbation theory. On the other hand, the dynamical (mainly nonperturbative) features of the hadron binding effects are encoded in correlators, which contain quark and gluon field operators, and can be parameterized in terms of light-cone wave functions and parton distribution functions. These quantities are process-independent and describe the universal interpolation between hadrons and their quark and gluon degrees of freedom as distributions over the fractions of * Corresponding author * * Speaker of the talk at the "Psi-to-Phi" Conference Email address: stefanis@tp2.ruhr-uni-bochum.de (N. G. Stefanis) the longitudinal and intrinsic transverse momenta carried by the partons. They have to be determined by nonperturbative methods (models), lattice calculations, or from the data.The (spacelike) transition form factors (TFFs) of pseudoscalar mesons, in particular the pion, have been extensively studied within QCD, because in leading order they are purely electromagnetic processes with the binding QCD effects being factorized out into the pion distribution amplitude (DA)-see [1] for a review and [2] for recent references. This means that for a highly virtual photon with the four-momentum transfer Q 2 and a quasi-real photon with q 2 → 0, the TFF can be cast as the convolution of the twist-two hard-scattering amplitude T (Q 2

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Section: Two-photon Processes For π 0 and η(η ′ ) In Qcdcontrasting

confidence: 83%

Pion-Photon Transition Form Factor and Pion Distribution Amplitude in QCD: Facing the Enigmatic Behavior of the BaBar Data

Stefanis

Bakulev²,

Михайлов³

et al. 2012

Nuclear Physics B - Proceedings Supplements

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“…The main idea which parallels the technique originally suggested in [14] for γ * γ → π transition form factor is to consider the hadronic tensor (2) at negative…”

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confidence: 99%

“…[14]) is that F V,A (q 2 , p 2 ), the generalized form factors of B → γ * ℓν ℓ , at fixed q 2 satisfy an unsubtracted dispersion relation in the variable p 2 . Separating the contribution of the lowest-lying vector mesons ρ, ω, one can write (…”

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confidence: 99%

“…If the separation between collinear and soft regions were done with an explicit cutoff, ω > µ 2 SC /E γ , the leading-order result for the form factors would read It is easy to see that the soft correction defined by (14), (15) effectively cuts off the small energy region in a way similar in spirit to (18), with the interval of duality playing the role of the hard cutoff µ SC . We therefore expect that the soft nonperturbative correction is always negative relative to the leading-order result because its role is, conceptually, to create a mass gap in the vector-meson mass spectrum.…”

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confidence: 99%

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Soft contribution to B→γℓνℓ and the B-meson distribution amplitude

Braun

Khodjamirian

2013

Physics Letters B

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The B → γℓν ℓ decay at large energies of the photon receives a numerically important soft-overlap contribution which is formally of the next-to-leading order in the expansion in the inverse photon energy. We point out that this contribution can be calculated within the framework of heavy-quark expansion and soft-collinear effective theory, making use of dispersion relations and quark-hadron duality. The soft-overlap contribution is obtained in a full analogy with the similar contribution to the γ * γ → π transition form factor. This result strengthens the case for using the B → γℓν ℓ decay to constrain the B-meson distribution amplitude and determine its most important parameter, the inverse moment λ B .1. The decay B → γℓν ℓ at large photon energy E γ is one of the simplest hadronic processes that can be studied using QCD factorization [1,2,3,4]. This method involves the B-meson light-cone distribution amplitude (DA) [5,6,7,8,9,10] as the main nonperturbative input at the leading order in the heavy quark expansion. The B → γℓν ℓ decay 1 is therefore best suited for determining the parameters of the B-meson DA and presents a close analog to the photon-pion transition γ * γ → π with one highly-virtual (Q 2 ) and one real photon, which is used for the determination of the pion DA. The theoretical challenges are also similar, and in both cases are mainly due to the necessity to have a quantitative control over the corrections that are subleading in the expansion parameter, 1/m b ∼ 1/(2E γ ) or 1/Q 2 , and, in general, are not factorizable. The purpose of this letter is to emphasize this connection and suggest a method to calculate the soft contribution to B → γℓν ℓ , which closely follows the technique used in γ * γ → π.A recent summary of the theory status of B → γℓν ℓ can be found in [11]. The decay amplitude1 to distinguish this important decay channel we suggest to call it photoleptonic B-decay.

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“…For g B * Bπ , there cannot be a direct experimental indication because there is no phase space for the B * → Bπ decay. Recently, a direct preliminary determination of g B * Bπ on the lattice has been attempted [5].The D * Dπ and B * Bπ couplings have been studied by several authors using different approaches of the QCD sum rules (QCDSR): two point function combined with soft pion techniques [6,7], light cone sum rules [8,9], light cone sum rules including perturbative corrections [10], sum rules in a external field [11], double momentum sum rules [12]. Unfortunately, the numerical results from these calculations may differ by almost a factor two.…”

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confidence: 99%

DDπ and BBπ form factors from QCD sum rules

Nielsen

Navarra

Bracco

et al. 2001

Nuclear Physics B - Proceedings Supplements

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The H * Hπ form factor for H = B and D mesons is evaluated in a QCD sum rule calculation. We study the Borel sum rule for the three point function of two pseudoscalar and one vector meson currents up to order four in the operator product expansion. The double Borel transform is performed with respect to the heavy meson momenta. We discuss the momentum dependence of the form factors and two different approaches to extract the H * Hπ coupling constant. PACS numbers 14.40.Lb, 14.40.Nd, 12.38.Lg, 11.55.Hx The coupling of the pion to the heavy mesons (g B * Bπ and g D * Dπ ) is related to the form factor at zero pionic momentum and its precise value has been often needed in phenomenology. In particular, the g D * Dπ coupling is needed in the context of quark gluon plasma (QGP) physics. Suppression of charmonium production in heavy ion collisions is one of the signatures of QGP formation [1]. Therefore a precise evaluation of the background, i.e., conventional J/ψ absorption by co-moving pions and ρ mesons [2], is of fundamental importance. Since pions are so abundant in a dense nuclear environment, the reactions π + J/ψ → D + D * (and consequently the coupling g D * Dπ ) are of special relevance [3].In the case of g D * Dπ , the D * + → D 0 π + decay is observed experimentally. However, present data provide only an upper bound: g D * Dπ ≤ 21 [4]. For g B * Bπ , there cannot be a direct experimental indication because there is no phase space for the B * → Bπ decay. Recently, a direct preliminary determination of g B * Bπ on the lattice has been attempted [5].The D * Dπ and B * Bπ couplings have been studied by several authors using different approaches of the QCD sum rules (QCDSR): two point function combined with soft pion techniques [6,7], light cone sum rules [8,9], light cone sum rules including perturbative corrections [10], sum rules in a external field [11], double momentum sum rules [12]. Unfortunately, the numerical results from these calculations may differ by almost a factor two.

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Form factors of

Cited by 130 publications

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Pion-Photon Transition Form Factor and Pion Distribution Amplitude in QCD: Facing the Enigmatic Behavior of the BaBar Data

Pion-Photon Transition Form Factor and Pion Distribution Amplitude in QCD: Facing the Enigmatic Behavior of the BaBar Data

Soft contribution to B→γℓνℓ and the B-meson distribution amplitude

DDπ and BBπ form factors from QCD sum rules

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Form factors of

Cited by 130 publications

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Pion-Photon Transition Form Factor and Pion Distribution Amplitude in QCD: Facing the Enigmatic Behavior of the BaBar Data

Pion-Photon Transition Form Factor and Pion Distribution Amplitude in QCD: Facing the Enigmatic Behavior of the BaBar Data

Soft contribution to B→γℓνℓ and the B-meson distribution amplitude

D*Dπ and B*Bπ form factors from QCD sum rules

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DDπ and BBπ form factors from QCD sum rules