Meson-Photon Transition Form Factors in the Charmonium Energy Range

The study of electron-positron collisions at center-of-mass energies corresponding to charmonium production has reached new levels of sensitivity thanks to experiments by the BES and CLEO Collaborations. Final states $\gamma P$,where$P$isapseudoscalarmesonsuchas$\pi^0$,$\eta$,and$\eta’$ can arise either from charmonium decays or in the continuum through a virtual photon: $e^{+}{e}^{-}\to {\gamma }^{\ast }\to \gamma P$. Estimates of this latter process are given at center-of-mass (c.m.) energies corresponding to the $J\mathrm{/}\psi (1S)$, $\psi (2S)$, and $\psi (3770)$ resonances.