Study of the electromagnetic Dalitz decays $ψ(Υ) \to η_{c}(η_{b}) l^{+} l^{-}$

Abstract

We study the electromagnetic Dalitz (EM) decays, $ψ\to η_{c} l^{+} l^{-}$ and $Υ\to η_{b} l^{+} l^{-}$ ($l = e$ or $μ$), in which the lepton pair comes from the virtual photon emitted by the M1 transition from $c\bar{c}$ ($b\bar{b}$) spin triplet state to the spin singlet state. We estimate the partial width of $ψ(Υ) \to η_{c}(η_{b}) l^{+} l^{-}$, based on the simple pole approximation. Besides, based on different QCD models, the partial width of $ψ(Υ) \to η_{c}(η_{b}) γ$ is determined.