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 c1 , 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.