Study of the Dalitz decay $J/\psi \to e^{+}{e}^{-}\eta$

Abstract

We report corrected results on a study of the electromagnetic Dalitz decay $J/\psi \to e^{+}{e}^{-}\eta$ and search for di-electron decays of a light dark gauge boson (${\gamma }^{\prime }$) in $J/\psi \to {\gamma }^{\prime }\eta$ with the two $\eta$ decay modes $\eta \to \gamma \gamma$ and $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$, using $(1310.6\pm 7.0)\times 10^6$ $J/\psi$ events collected with the BESIII detector. In particular we update the measurement of the pole mass of the transition form factor (TFF) of $J/\psi \to e^{+}{e}^{-}\eta$ to be $\Lambda =2.56\pm 0.04(\mathrm{stat})\pm 0.03(\mathrm{syst})$ GeV/$c^2$. The branching fraction of $J/\psi \to e^{+}{e}^{-}\eta$ and the kinetic-mixing strength between the Standard Model photon and ${\gamma }^{\prime }$ are also updated after taking the corrected $\Lambda$ value into account. The measured branching fraction of $J/\psi \to e^{+}{e}^{-}\eta$ is updated to be $(1.42\pm 0.04(\mathrm{stat})\pm 0.07(\mathrm{syst}))\times 10^{-5}$, where the first and second uncertainties are statistical and systematic, respectively.

6 pages, 3 figures, Erratum of Phys. Rev. D 99, 012006 (2019)