We calculate the contributions from QED processes involving two virtual photons to the cross sections for e +e - annihilation into two charmonium states with the same C parity. Genetically, the cross sections are three orders of magnitude smaller than those for charmonia with opposite C parity because they are suppressed by a factor of α 2/ α s 2. However, if both charmonia have quantum numbers J pc = 1 -, then there is a contribution to the cross section that involves the fragmentation of each photon into a charmonium. The fragmentation contribution is enhanced by powers of E beam/m c, the ratio of the beam energy to the charm-quark mass, and this enhancement can compensate for the suppression factor that is associated with the coupling constants. In particular, the predicted cross section for J/ψ+J/ψ at the B factories is larger than that for J/ψ + η c.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)
- General Physics and Astronomy
- Nuclear and High Energy Physics
- Mathematical Physics