Eur. Phys. J. A (2010) 46: 197-205
https://doi.org/10.1140/epja/i2010-11029-6

Regular Article - Theoretical Physics

The pion transition form factor and the pion distribution amplitude

Departamento de Fisica Teorica and Instituto de Fısica Corpuscular, Universidad de Valencia-CSIC, E-46100 Burjassot, Valencia, Spain

^* e-mail: Vicente.Vento@uv.es

Received: 24 June 2010
Accepted: 23 August 2010
Published online: 23 September 2010

Abstract

Recent BaBar data on the pion transition form factor, whose Q²-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 description for low photon virtuality and a high photon virtuality description based on QCD, which match at a scale Q₀. The high photon virtuality description incorporates a flat pion distribution amplitude, (x) = 1 , at the matching scale Q₀ and QCD evolution from Q₀ to Q > Q ₀ . The flat pion distribution is connected, through soft pion theorems and chiral symmetry, to the pion valence parton distribution at the same low scale Q₀. The procedure leads to a good description of the data, and by incorporating additional twist-three effects, to an excellent description of the data.