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 JP = 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 1, η(2S), and η(1S) 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 Q2, the Landau--Yang suppression factors of the two-photon cross sections being compensated by the photon propagators.
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