Аннотация
The two-photon transition \$\psi' \gammaJ/\psi\$ is studied in a
sample of 106 million \$\psi'\$ decays collected by the BESIII detector. The
branching fraction is measured to be
\$(3.3\pm0.6(stat)^+0.8\_-1.1(syst)) \times10^-4\$ using
\$J/e^+e^-\$ and \$J/\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'\to\gamma\chi\_cJ\$, \$\chi\_cJ\to\gamma
J/(J=0,1,2)\$ are reported.
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