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

Abstract

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 ${\mathcal{B}}_{Z\to J/\psi +J/\psi }$ ~ 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 ${\mathcal{B}}_{Z\to J/\psi +J/\psi }$ = (${1.110}_{-0.241-0.001}^{+0.334+0.054}$) × 10⁻¹⁰, which displays a fairly steady dependence on the renormalization scale, is significantly lower than the upper limits released by CMS.