Improved analysis of rare $Z$-boson decays into a heavy vector quarkonium plus lepton pair

Li Ang, Dao-Neng Gao

We improve the theoretical predictions for rare $Z$-boson decays, $Z\to V{\ell }^{+}{\ell }^{-}$ ($\ell =e$ or $\mu$), where $V$ denotes a heavy vector quarkonium including $J/\Psi$, $\Psi (2S)$, and…