Observation of $e^{+}e^{-} \to \eta^{\prime} J/\psi$ at center-of-mass   energies between 4.189 and 4.600 GeV
  The process $e^{+}e^{-}\to \eta^{\prime} J/\psi$ is observed for the first time with a statistical significance of $8.6\sigma$ at center-of-mass energy $\sqrt{s} = 4.226$ GeV and $7.3\sigma$ at $\sqrt{s} = 4.258$ GeV using data samples collected with the BESIII detector. The Born cross sections are measured to be $(3.7 \pm 0.7 \pm 0.3)$ and $(3.9 \pm 0.8 \pm 0.3)$ pb at $\sqrt{s} = 4.226$ and $4.258$ GeV, respectively, where the first errors are statistical and the second systematic. Upper limits at the 90% confidence level of the Born cross sections are also reported at other 12 energy points. 
M. Ablikim, M. N. Achasov, S.Ahmed, X. C. Ai, O. Albayrak, M.   Albrecht, D. J. Ambrose, A. Amoroso, F. F. An, Q. An, J. Z. ...
hep-ex