The form factor FA(0) in π→eνγ is calculated, at the soft pion point, directly from data on the semileptonic τ-lepton decays τ→ντ + nπ, which determine the relevant vector and axial-vector hadronic spectral functions. The reliability of this calculation is assessed by using these fitted spectral functions to check the saturation of the first two Weinberg sum rules. The results are: FA(0)=0.017±0.004, and γ(0)FA(0)/FV(0)=0.67±0.04±0.16. © 1988.
|Journal||Physics Letters B|
|Publication status||Published - 7 Jul 1988|