Observation of $J/\psi$ Electromagnetic Dalitz Decays to $X(1835)$, $X(2120)$ and $X(2370)$

Abstract

Using a sample of about 10 billion $J/\psi$ events collected at a center-of-mass energy $\sqrt{s}=3.097$ 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 the 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.

Comments: 9 pages, 3 figures