Four-lepton decays of neutral vector mesons

Wen Chen,Xiaonu Xiong,Zhewen Mo,Yu Jia,Jichen Pan

doi:10.1103/physrevd.104.094023

Abstract

We investigate the rare electromagnetic decays of neutral vector mesons (exemplified by $J/\psi$, $\Upsilon$, $\rho^0$, $\omega,\phi$, \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 $J/\psi(\Upsilon)\to 2(e^+e^-), e^+e^-\mu^+\mu^-$ 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.

Highlights

The leptonic decays of neutral vector mesons are arguably one of the cleanest and most exhaustively studied hadronic processes
We investigate the rare electromagnetic decays of neutral vector mesons into four charged leptons [2ðeþe−Þ, 2ðμþμ−Þ, 2ðτþτ−Þ, eþe−μþμ−, eþe−τþτ−, ...] 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 cut off the mass singularity

Summary

Introduction

The leptonic decays of neutral vector mesons are arguably one of the cleanest and most exhaustively studied hadronic processes. To dematerialize into a lepton pair, the valence quark and antiquark inside the vector meson have to first annihilate into a virtual photon, which subsequently transition into a lepton pair. Since the hadronic decay part and the electromagnetic production part of the amplitude factorizes, one can write down the well-known formula for vector meson leptonic decay: ΓðV → eþe−Þ 1⁄4 4πe2qα2f2V 3MV. ; ð1Þ where α denotes the fine structure constant, and eq signifies the electric charge of the valence quark of V. MV denotes the vector meson mass, associated with V1: and fV denotes the decay constant h0jqγμqjVðPÞi 1⁄4 fV MVεμ ðPÞ; ð2Þ 3 πMV.

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Results

Conclusion