Observation of $e^{+}{e}^{-}\to \eta J/\psi$ at center-of-mass energy $sqrts=4.009$ GeV

The BESIII Collaboration, M. Ablikim, M. N. Achasov +339

Using a 478 pb${}^{-1}$ data sample collected with the BESIII detector operating at the BEPCII storage ring at a center-of-mass energy of $\sqrt{s}=4.009$ GeV, the production of $e^{…