Meson - photon transition form factors

Jakob, R.; Kroll, P.; Raulfs, M

doi:10.1088/0954-3899/22/1/004

Cited by 100 publications

(193 citation statements)

References 45 publications

(91 reference statements)

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“…It has been advocated in [18,20,21,23,25,42,67,79] that at momentum-transfer values probed experimentally so far, this latter contribution, though power suppressed because it behaves like 1/Q 4 for large Q 2 , dominates and mimics rather well the observed 1/Q 2 behavior. To account for this effect, we will include the soft contribution [25] (discussed in Sec.…”

Section: Qcd Factorization Applied To the Pion Form Factormentioning

confidence: 70%

“…While it may still be not possible to clarify all these theoretical issues conclusively, we believe that significant progress has quite recently been achieved in understanding the pion structure both from the theoretical side-perturbatively [26,27,28,29,30] and nonperturbatively [1, 31,32,33,34]-as well as from the experimental side [35,36,37] and associated data-processing techniques [38,39,40], a progress that could bring to a cleaner comparison between data and various theoretical QCD predictions [31,39,40,41,42,43,44,45,46,47,48,49]. 1 Moreover, a program to compute the electromagnetic and transition form factors of mesons on the lattice has been launched by two collaborations, [51,52] and [53], that may provide valuable insights when it is completed.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Publisher's Note: Pion form factor in QCD: From nonlocal condensates to next-to-leading-order analytic perturbation theory [Phys. Rev. D 70, 033014 (2004)]

Bakulev¹,

Passek‐Kumerički²,

Schroers³

et al. 2004

Phys. Rev. D

118

252

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We present an investigation of the pion's electromagnetic form factor F π (Q 2 ) in the spacelike region utilizing two new ingredients: (i) a double-humped, endpoint-suppressed pion distribution amplitude derived before via QCD sum rules with nonlocal condensates-found to comply at the 1σ level with the CLEO data on the πγ transition-and (ii) analytic perturbation theory at the level of parton amplitudes for hadronic reactions. The computation of F π (Q 2 ) within this approach is performed at NLO of QCD perturbation theory (standard and analytic), including the evolution of the pion distribution amplitude at the same order. We consider the NLO corrections to the form factor in the MS scheme with various renormalization scale settings and also in the α Vscheme. We find that using standard perturbation theory, the size of the NLO corrections is quite sensitive to the adopted renormalization scheme and scale setting. The main results of our analysis are the following: (i) Replacing the QCD coupling and its powers by their analytic images, both dependencies are diminished and the predictions for the pion form factor are quasi scheme and scale-setting independent. (ii) The magnitude of the factorized pion form factor, calculated with the aforementioned pion distribution amplitude, is only slightly larger than the result obtained with the asymptotic one in all considered schemes. (iii) Including the soft pion form factor via local duality and ensuring the Ward identity at Q 2 = 0, we present predictions that are in remarkably good agreement with the existing experimental data both in trend and magnitude.

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Section: Qcd Factorization Applied To the Pion Form Factormentioning

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Publisher's Note: Pion form factor in QCD: From nonlocal condensates to next-to-leading-order analytic perturbation theory [Phys. Rev. D 70, 033014 (2004)]

Bakulev¹,

Passek‐Kumerički²,

Schroers³

et al. 2004

Phys. Rev. D

118

252

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“…͑48͒ provides the result for the quark distribution, which in the massless case (m 2 ϭϪp 2 ϭ0) is reduced to 7 For details, see Ref.…”

Section: Quark Distribution Function and Its Qcd Evolutionmentioning

confidence: 99%

Pion structure function within the instanton model

2000

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The leading-twist valence-quark distribution function in the pion is obtained at a low normalization scale of an order of the inverse average size of an instanton c . The momentum dependent quark mass and the quark-pion vertex are constructed in the framework of the instanton liquid model, using a gauge invariant approach. The parameters of instanton vacuum, the effective instanton radius and quark mass, are related to the vacuum expectation values of the lowest dimension quark-gluon operators and to the pion low energy observables. An analytic expression for the quark distribution function in the pion for a general vertex function is derived. The results are QCD evolved to higher momentum-transfer values, and reasonable agreement with phenomenological analyses of the data on parton distributions for the pion is found.

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“…Hadronic form factors and Compton scattering, for example, are dominated by soft contributions at presently accessible c.m. energies [9][10][11]. In this talk we will discuss Sudakov suppressions in γγ → π + π − in the few GeV region and point out the difference between our approach and that of Ref.…”

mentioning

confidence: 99%

Two-photon annihilation into pion pairs

Vogt

2001

AIP Conference Proceedings

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Abstract. We discuss pion pair production in two-photon collisions in two different kinematical regimes. When both photons are real and at moderately large center-ofmass energy √ s we elaborate on partonic transverse momentum and Sudakov corrections within the hard scattering approach. We also point out the difference between our approach and that of other authors. When one of the photons is highly virtual the produced pion pair can be described in terms of a two-pion distribution amplitude, for which we derive the perturbative limit at large s.Due to the pointlike structure of the photon exclusive hadron production in twophoton collisions provides a very useful field for the test of perturbative QCD. In the limit of large √ s, the amplitude of γ ( * ) γ → ππ factorises into a perturbatively calculable hard photon-parton scattering, which in lowest order can simply be obtained from one-gluon exchange diagrams, and soft parts that are expressed in terms of distribution amplitudes describing the transition of partons to pions [1].At large c.m. energies √ s, transverse momenta of the partons relative to the pion are negligible and the conventional collinear hard scattering formula can be applied [2]. At moderately large √ s of a few GeV, however, the collinear approach is known to suffer severely from substantial endpoint contributions where the strong coupling α s becomes large, such that perturbation theory is not applicable [3]. These problems can be overcome by including transverse momenta and Sudakov corrections [4,5]. The correspondingly modified hard scattering approach leads to perturbative predictions, which in most cases are not sufficient to account for the experimental data [6][7][8]. Hadronic form factors and Compton scattering, for example, are dominated by soft contributions at presently accessible c.m. energies [9][10][11]. In this talk we will discuss Sudakov suppressions in γγ → π + π − in the few GeV region and point out the difference between our approach and that of Ref. [12].

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Meson - photon transition form factors

Cited by 100 publications

References 45 publications

Publisher's Note: Pion form factor in QCD: From nonlocal condensates to next-to-leading-order analytic perturbation theory [Phys. Rev. D 70, 033014 (2004)]

Publisher's Note: Pion form factor in QCD: From nonlocal condensates to next-to-leading-order analytic perturbation theory [Phys. Rev. D 70, 033014 (2004)]

Pion structure function within the instanton model

Two-photon annihilation into pion pairs

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