摘要
Within the standard model,we have investigated rare Z-boson decays into double heavy quarkonia,Z→VV and Z→VP,with V and P denoting vector and pseudo scalar quarkonia,respectively.It is assumed that the leading-order QCD diagrams would give the dominant contributions to these processes,and the corresponding branching fractions,for instance,B(Z→J/ΨJ/Ψ),have been estimated to be approximately 10^(-13)in literature.However,these decays could also happen through electromagnetic transitions Z→Vγ^(*)and Z→Pγ^(*),with the virtual photon transforming into V.Interestingly,the smallness of the vector quarkonium mass can give rise to a large factor m_(Z)^(2)/m_(V)^(2)relative to the QCD contributions,which thus counteracts the suppression from the electromagnetic coupling.We systematically include these two types of contributions in our calculation to predict branching fractions for these decays.Particularly,owing to the virtual photon effects,it is found that B(Z→J/ΨJ/Ψ)will be significantly enhanced,up to 10^(-10).
作者
高道能
龚玺
Dao-Neng Gao;Xi Gong(Interdisciplinary Center for Theoretical Study,University of Science and Technology of China,Hefei 230026,China;Peng Huanwu Center for Fundamental Theory,Hefei 230026,China)
基金
Supported in part by the National Natural Science Foundation of China(11575175,12047502)
National Research and development Program of China(2020YFA0406400)。