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

Abstract

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 $e^{+}{e}^{-}\to \eta J\psi$ is observed for the first time with a statistical significance of greater than $10\sigma$. The Born cross section is measured to be $(32.1\pm 2.8\pm 1.3)$ pb, where the first error is statistical and the second systematic. Assuming the $\eta J\psi$ signal is from a hadronic transition of the $\psi (4040)$, the fractional transition rate is determined to be $\mathcal{B}(\psi (4040)\to \eta J\psi )=(5.2\pm 0.5\pm 0.2\pm 0.5)\times 10^{-3}$, where the first, second, and third errors are statistical, systematic, and the uncertainty from the $\psi (4040)$ resonant parameters, respectively. The production of $e^{+}{e}^{-}\to {\pi }^{0}J\psi$ is searched for, but no significant signal is observed, and $\mathcal{B}(\psi (4040)\to {\pi }^{0}J\psi )<2.8\times 10^{-4}$ is obtained at the 90% confidence level.

7 pages, 5 figures

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• Heavy quarkonium: progress, puzzles, and opportunities
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• Measurement of e^+e^- to pi^+pi^-J/psi Cross Section via Initial State Radiation at Belle

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