We calculate the next-to-leading-order corrections to the perturbative QCD calculation of the decay $\frac{J}{\psi }\to {\pi }^{+}{\pi }^{-}$ that cannot be factorized into either initial or final state wave functions. When using either the asymptotic or Chernyak-Zhitnitsky distribution amplitudes for the pion we find that these corrections are small (∼ 5%). Since the leading process is proportional to $F_{\pi }^2\left(M_J^2\right)$, we suggest that the pion form factor at a large timelike $Q^2$ can be extracted from the measured decay rate of charmonium. Normalizing to the corresponding leptonic decay channels, we thus obtain that $M_J^2{F}_{\pi }\left(M_J^2\right)\approx 0.9$, approximately a factor of 2 larger than what might have been commonly expected.

• Received 23 November 1992

DOI:https://doi.org/10.1103/PhysRevD.47.R3690