$\eta$ and $\eta'$ transition form factors from Pad\'e approximants
  We employ a systematic and model-independent method to extract, from space- and time-like data, the $\eta$ and $\eta'$ transition form factors (TFFs) obtaining the most precise determination for their low-energy parameters and discuss the $\Gamma_{\eta\rightarrow\gamma\gamma}$ impact on them. Using TFF data alone, we also extract the $\eta-\eta'$ mixing parameters, which are compatible to those obtained from more sophisticated and input-demanding procedures. 
Pablo Sanchez-Puertas and Pere Masjuan
hep-ph hep-ex