QCD sum rule calculation of γγ* → π0 transition form factor

Abstract

We discuss QCD sum rule analysis of the form factor Fγ * γ * π o ( q 2 , Q 2 ) in the region where virtuality of one of the spacelike photons is small q 2 ≪ 1 GeV 2 while another is large: Q 2 ≳ 1 GeV 2 . Our approach, in contrast to pQCD, does not require explicit assumptions about the shape of the pion distribution amplitude φ π ( X ). The absolute value of the 1/ Q 2 term obtained in this paper favours φ π ( X ) close to the asymptotic form φ π as ( X ) = 6 ƒ π x (1 − x).