Production of J / ψ + η(c) versus J / ψ + J / ψ at the LHC: importance of real α(s)(5) corrections.

We proceed for the first time to the evaluation of the Born cross section for J / ψ + η(c) production, namely, via g + g → J/ψ+ η(c) + g, and show that it has a harder P(T) spectrum than the J/ψ-pair yield at the Born level. If one stuck to a comparison at the Born level, one would conclude that J / ψ + η(c) production would surpass that of J / ψ + J / ψ at large P(T). This is nonetheless not the case since J / ψ-pair production, as for single J / ψ, receives leading-P(T) contributions at higher orders in α(s). We also present the first evaluation of these leading-P(T) next-to-leading order contributions. These are indeed significant for increasing P(T) and are of essential relevance for comparison with forthcoming data. We also compute kinematic correlations relevant for double-parton-scattering studies. Finally, we evaluate the polarization of a J/ψ accompanied by either an η(c) or a J/ψ and another light parton. These results may be of great help to understand the polarization of quarkonia produced at high energies.