Abstract
We report results on the transition form factor obtained within the hard scattering approach including transverse momentum effects and Sudakov corrections. The results clearly favour distribution amplitudes close to the asymptotic form, , and disfavour distribution amplitudes which are strongly concentrated in the end-point regions. This observation is backed by information on the elastic form factor of the pion and on its valence-quark distribution function. Applications of our approach to the and transition form factors are discussed as well. Combining the form factor data with the two-photon decay widths, we determine the and the decay constants and the mixing angle.
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