Four-lepton decays of neutral vector mesons

TL;DR

This paper calculates the rare four-lepton decay rates of neutral vector mesons like J/ψ and Υ, highlighting the importance of lepton mass effects and predicting observable branching fractions at current experiments.

Contribution

It provides the first detailed lowest-order QED calculations of four-lepton decay channels for neutral vector mesons, including lepton mass effects and branching fraction estimates.

Findings

Branching fractions for J/ψ and Υ decays into four leptons are around 10^{-5}.

Decays into electron pairs are significantly more probable than into muon pairs.

Predicted decay rates are within reach of BESIII, Belle 2, and LHC experiments.

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.