The two-photon transition $psi’ o gammagamma J/psi$ is studied in a
sample of 106 million $psi’$ decays collected by the BESIII detector. The
branching fraction is measured to be
$(3.3pm0.6(unit{stat})^{+0.8}_{-1.1}(unit{syst})) imes10^{-4}$ using
$J/psi o e^+e^-$ and $J/psi o mu^+mu^-$decays. This work represents the
first measurement of a two-photon transition among charmonium states. The
orientation of the $psi’$ decay plane and the $J/psi$ polarization in this
decay are also studied. In addition, the product branching fractions of
sequential $E1$ transitions $psi’ ogammachi_{cJ}$, $chi_{cJ} ogamma
J/psi (J=0,1,2)$ are reported.
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