Four-lepton decays of neutral vector mesons

Abstract

We investigate the rare electromagnetic decays of neutral vector mesons (exemplified by $J/\psi$, ${\rm Y}$, ${\rho }^0$, $\omega ,\varphi$, \ldots) into four charged leptons ($2(e^{+}{e}^{-})$, $2({\mu }^{+}{\mu }^{-})$, $2({\tau }^{+}{\tau }^{-})$, $e^{+}{e}^{-}{\mu }^{+}{\mu }^{-}$, $e^{+}{e}^{-}{\tau }^{+}{\tau }^{-}$, \ldots) at lowest order in QED. In contrast to the case of vector meson decay into a single pair of leptons, the lepton mass must be retained in these four-lepton decay channels to cutoff the mass singularity. Owing to more pronounced collinear enhancement, the branching fractions of vector mesons decays into $2(e^{+}{e}^{-})$ are considerably greater than those for decays into $2({\mu }^{+}{\mu }^{-})$. The decay channels $J/\psi ({\rm Y})\to 2(e^{+}{e}^{-}),e^{+}{e}^{-}{\mu }^{+}{\mu }^{-}$ are predicted to have branching fractions of order $10^{-5}$, which appear to have bright observation prospect at {\tt BESIII}, {\tt Belle 2} and {\tt LHC} experiments.

Comments: 10 pages, 6 figures, 4 tables