Study of the electromagnetic Dalitz decays $\psi ({\rm Y})\to {\eta }_c({\eta }_b)l^{+}{l}^{-}$

Abstract

We study the electromagnetic Dalitz (EM) decays, $\psi \to {\eta }_c{l}^{+}{l}^{-}$ and ${\rm Y}\to {\eta }_b{l}^{+}{l}^{-}$ ($l=e$ or $\mu$), 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 $\psi ({\rm Y})\to {\eta }_c({\eta }_b)l^{+}{l}^{-}$, based on the simple pole approximation. Besides, based on different QCD models, the partial width of $\psi ({\rm Y})\to {\eta }_c({\eta }_b)\gamma$ is determined.