Using a sample of about ${10}^{10}J/\psi$ events collected at a center-of-mass energy $\sqrt{s}=3.097\mathrm{GeV}$ with the BESIII detector, the electromagnetic Dalitz decays $J/\psi \to e^{+}{e}^{-}{\pi }^{+}{\pi }^{-}{\eta }^{\prime }$, with ${\eta }^{\prime }\to \gamma {\pi }^{+}{\pi }^{-}$ and ${\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}\eta$, have been studied. The decay $J/\psi \to e^{+}{e}^{-}X(1835)$ is observed with a significance of $15\sigma$, and also an $e^{+}{e}^{-}$ invariant-mass dependent transition form factor of $J/\psi \to e^{+}{e}^{-}X(1835)$ is presented for the first time. The intermediate states $X(2120)$ and $X(2370)$ are also observed in the ${\pi }^{+}{\pi }^{-}{\eta }^{\prime }$ invariant-mass spectrum with significances of $5.3\sigma$ and $7.3\sigma$. The corresponding product branching fractions for $J/\psi \to e^{+}{e}^{-}X$, $X\to {\pi }^{+}{\pi }^{-}{\eta }^{\prime }$ [$X=X(1835)$, $X(2120)$, and $X(2370)]$ are reported.

• Received 30 December 2021
• Revised 7 April 2022
• Accepted 8 June 2022

DOI:https://doi.org/10.1103/PhysRevLett.129.022002

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Published by the American Physical Society