Analysis of double-J/ψ production in Z decay at next-to-leading-order QCD accuracy

A bstract In this article, we study in detail the double- J/ψ yield through Z decay at the next-to-leading-order (NLO) QCD accuracy within the nonrelativistic QCD factorization. At the tree level, the pure QCD diagrams predict a branching ratio of B Z → J / ψ + J / ψ ~ 10 − 12 ; however, the inclusion of the QED diagrams would augment this prediction by approximately 2–3 orders of magnitude. After incorporating the QCD corrections, the QCD results exhibit a considerable increase, whereas the QED results undergo a substantial reduction. Combining the QCD and QED contributions at NLO in α s , it is observed that the prediction of B Z → J / ψ + J / ψ = ( 1.110 − 0.241 − 0.001 + 0.334 + 0.054 ) × 10 − 10 , which displays a fairly steady dependence on the renormalization scale, is significantly lower than the upper limits released by CMS.