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
Accepted: 23 August 2010
Published online: 23 September 2010
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.
© SIF, Springer-Verlag Berlin Heidelberg, 2010