Light-cone sum rules for the D(s) → η(′)lνl form factor

We present an improved light-cone sum rule analysis of the decay form factors of D and D-s into eta and eta' and argue that these decays offer a very promising possibility to determine the leading Fock-state gluonic contribution of the eta' at future experimental facilities such as FAIR or Super-KEKB. We also give the corresponding branching ratios for B decays.