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The two-photon transition $\psi(3686)\to\gamma\gamma J/\psi$ is studied in asample of 106 million $\psi(3686)$ decays collected by the BESIII detector. Thebranching fraction is measured to be$(3.1\pm0.6(\unit{stat})^{+0.8}_{-1.0}(\unit{syst})) \times10^{-4}$ using$J/\psi\to e^+e^-$ and $J/\psi\to\mu^+\mu^-$ decays, and its upper limit isestimated to be $4.5\times10^{-4}$ at the 90% conference level. This workrepresents the first measurement of a two-photon transition among charmoniumstates. The orientation of the $\psi(3686)$ decay plane and the $J/\psi$polarization in this decay are also studied. In addition, the product branchingfractions of sequential $E1$ transitions $\psi(3686)\to\gamma\chi_{cJ},\chi_{cJ}\to\gamma J/\psi (J=0,1,2)$ are reported.

Evidence for the Direct Two-Photon Transition from $\psi(3686)$ to $J/\psi$