Meson photon transition form-factors and resonance cross-sections in e+ e- collisions

Abstract Meson-photon-photon transition form factors for S -, P -, and D -wave states are calculated, the meson being treated as a non-relativistic heavy-quark-antiquark pair. The full dependence on both photon virtualities is included. Cross-section formulas for charge-conjugation even mesons with J p = 0 − , 0 + , 1 + , 2 + , and 2 − in electron-positron collisions are presented and numerical results for LEP energies are given. In particular, we find two-photon event rates for χ c 1 , η c (2 S ), and η b (1 S ) within reach of LEP. With minor modifications to incorporate SU (3)-flavour breaking we estimate rates for 18 light mesons as well, based on the observation that their two-photon decay widths agree remarkably well with measured data. Finally we point out that e + e − cross sections for 1 + states do not vanish at low Q 2 , the Landau-Yang suppression factors of the two-photon cross sections being compensated by the photon propagators.