What can be learned from the transition form factor of

We present an analysis of the recent measurement of $$\eta '$$-meson production by two virtual photons made by the BaBar collaboration. It is the first measurement of a transition form factor which is entirely within the kinematic regime of the collinear factorization approach, and it thus provides a clean test of the QCD factorization theorem for distribution amplitudes (DAs). We demonstrate that the data are in agreement with perturbative QCD. Also we show that it is sensitive to power corrections to the factorization theorem and to the decay constants. We discuss features of the meson production cross-section and point out the kinematic regions that are sensitive to interesting physics. We also provide an estimation of uncertainties on the extraction of DA parameters