The pion transition form factor and the pion distribution amplitude

Abstract

Recent BaBaR data on the pion transition form factor, whose Q^2 dependence is much steeper then predicted by asymptotic Quantum Chromodynamics (QCD), have caused a renewed interest in its theoretical description. We present here a formalism based on a model independent low energy description and a high energy description based on QCD, which match at a scale Q_0. The high energy description incorporates a flat pion distribution amplitude, phi(x)=1, at the matching scale Q_0 and QCD evolution from Q_0 to Q>Q_0. The flat pion distribution is connected, through soft pion theorems and chiral symmetry, to the pion valance parton distribution at the same low scale Q_0. The procedure leads to a good description of the data, and incorporating additional twist three effects, to an excellent description of the data.

11 pages, 5 postscript figures, uses epsfig.sty and 1 appendix

References in corpus (7)

• Measurement of the gamma gamma* --> pi0 transition form factor
• Moments of pseudoscalar meson distribution amplitudes from the lattice
• Shape of Pion Distribution Amplitude
• On the Pion Distribution Amplitude Shape
• Generalized parton distributions of the pion in chiral quark models and their QCD evolution
• Pion transition form factor at the two-loop level vis-à-vis experimental data
• The Pion-Photon Transition Distribution Amplitudes in the Nambu-Jona Lasinio Model

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