Ablikim, M (reprint author), Inst High Energy Phys, Beijing 100049, Peoples R China.
The two-photon transition psi(3686) -> gamma gamma J/psi is studied in a sample of 1.06 x 10(8) psi(3686) decays collected by the BESIII detector. The branching fraction is measured to be (3.1 +/- 0.6(stat)(-1.0)(+0.8)(syst)) x 10(-4) using J/psi -> e(+)e(-) and J/psi -> mu(+)mu(-) decays, and its upper limit is estimated to be 4.5 x 10(-4) at the 90% confidence level. This work represents the first measurement of a two-photon transition among charmonium states. The orientation of the psi(3686) decay plane and the J/psi polarization in this decay are also studied. In addition, the product branching fractions of sequential E1 transitions psi(3686) -> gamma chi(cJ) and chi(cJ) -> gamma J/psi (J = 0, 1, 2) are reported.