Study of the electromagnetic Dalitz decays psi(Upsilon) -> eta(c)(eta(b))l(+) l(-)

We study the electromagnetic Dalitz decays, psi -> eta(c)l(+) l(-) and Upsilon -> 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 (c) over bar (b (b) over bar) spin triplet state to the spin singlet state. We estimate the partial width of psi(Upsilon) -> eta(c)(eta(b))l(+) l(-), based on the simple pole approximation. Besides, based on different QCD models, the partial width of psi(Upsilon) -> eta(c)(eta(b))gamma is determined.