Resummation of relativistic corrections to exclusive productions of charmonia in e+^e- collisions

We investigate two exclusive processes, e⁺e ^-→η_c+γ and e⁺e ^-→J/ψ+J/ψ, at the center-of-momentum energy √s=10.58 GeV within the framework of the nonrelativistic QCD factorization approach. A class of relativistic corrections is resummed to all orders in the heavy-quark velocity v and the corrections are large negative. We further improve the prediction by including available QCD next-to-leading-order corrections and the interference between the QCD and relativistic corrections. The prediction for σ[e⁺e^-→η _c+γ] is about 50 fb. In the case of e⁺e ^-→J/ψ+J/ψ the standard nonrelativistic QCD prediction for the cross section is negative. As an alternative, the vector-meson-dominance approach is employed to compute the photon-fragmentation contribution of the process, which gives the cross section ∼1 fb. This is an indication that the uncalculated QCD higher-order corrections may be significant. Our results can be tested against the forthcoming data from Belle II and super B factories.