Exclusive processes in perturbative quantum chromodynamics

Abstract

We present a systematic analysis in perturbative quantum chromodynamics (@CD) of large-momentum-transfer exclusive processes. Predictions are given for the scaling behavior, angular dependence, helicity structure, and normalization of elastic and inelastic form factors and large-angle exclusive scattering amplitudes for hadrons and photons. We prove that these reactions are dominated by quark and gluon subprocesses at short distances, and thus that the dimensional-counting rules for the power-law falloff of these amplitudes with momentum transfer are rigorous predictions of @CD, modulo calculable logarithmic corrections from the behavior of the hadronic wave functions at short distances. These anomalous-dimension corrections are determined by evolution equations for process-independent meson and baryon "distribution amplitudes" Si(x, ,g) which control the valence-quark distributions in high-momentum-transfer exclusive reactions. The analysis can be carried out systematically in powers of a, (Q'), the QCD running coupling constant. Although the calculations are most conveniently carried out using light-cone perturbation theory and the light-cone gauge, we also present a gauge-independent analysis and relate the distribution amplitude to a gauge-invariant Bethe-Salpeter amplitude.

Study of pure annihilation type decaysB D sK

“…The functions h a , h (1) a , and h (2) a in the decay amplitudes consist of two parts: one is the jet function S t (x i ) derived by the threshold resummation [15], the other is the propagator of virtual quark and gluon. They are defined by…”

“…Perturbative QCD (PQCD) method for B decays has been developed for some years [1]. It is successfully applied to exclusive B meson decays recently, such as B → ππ [2], B → Kπ [3], B → πρ [4] and other channels [5].…”

Light-Front Quark Model Analysis of the \((\pi ^{0},\eta ,\eta ') \to \gamma ^{*}\gamma \) Transition Form Factors

“…It can be calculated asymptotically at leading twist as a convolution of a perturbative hard scattering amplitude and a gaugeinvariant meson distribution amplitude (DA) which incorporates the nonperturbative dynamics of QCD bound state [1]. The prediction for F πγ (Q 2 ) at the asymptotic limit Q 2 → ∞ is shown to satisfy the Brodsky-Lepage limit [1]: Q 2 F πγ (Q 2 → ∞) = √ 2f π GeV with f π 130 MeV.…”

“…It can be calculated asymptotically at leading twist as a convolution of a perturbative hard scattering amplitude and a gaugeinvariant meson distribution amplitude (DA) which incorporates the nonperturbative dynamics of QCD bound state [1]. The prediction for F πγ (Q 2 ) at the asymptotic limit Q 2 → ∞ is shown to satisfy the Brodsky-Lepage limit [1]: Q 2 F πγ (Q 2 → ∞) = √ 2f π GeV with f π 130 MeV. However, the data for Q 2 F πγ (Q 2 ) measured from the γ * γ → π 0 process by the BaBar Collaboration in 2009 [2] have shown not only the serious violation of the Brodsky-Lepage limit but also the rapid growth for Q 2 > 15 GeV 2 .…”

B0→ωη(′)andϕη(′Guo1, Chen2, Xiao3 2007Phys. Rev. D220140View full textAdd to dashboardCite

“…At present, there exist two popular factorization approaches to calculate the hadronic matrix element < M 1 M 2 |O i |B >: the QCDF approach [2] and the pQCD approach [3,14,15]. The pQCD approach has been developed earlier from the QCD hard-scattering approach [15].…”