Observation of the Dalitz Decay ${\eta }^{\prime }\to \gamma e^{+}{e}^{-}$

M. Ablikim, M. N. Achasov, X. C. Ai +410

We report the first observation of the Dalitz decay ${\eta }^{\prime }\to \gamma e^{+}{e}^{-}$, based on a data sample of 1.31 billion $J/\psi$ events collected with the BESIII detector. The ${\eta }^{\prime }$ mesons are pr…