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 BZ→J/ψ+J/ψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\mathcal{B}}_{Z\ o J/\\psi +J/\\psi } $$\\end{document} ~ 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 αs, it is observed that the prediction of BZ→J/ψ+J/ψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\mathcal{B}}_{Z\ o J/\\psi +J/\\psi } $$\\end{document} = (1.110−0.241−0.001+0.334+0.054\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {1.110}_{-0.241-0.001}^{+0.334+0.054} $$\\end{document}) × 10−10, which displays a fairly steady dependence on the renormalization scale, is significantly lower than the upper limits released by CMS.