Measurement of the γ∗γ∗ →η′ transition form factor

We study the process e^+e^− → e^+e^−η′ in the double-tag mode and measure for the first time the γ⋆γ⋆ → η′ transition form factor F_η′(Q^2_1,Q^2_2) in the momentum-transfer range 2 < Q^2_1, Q^2_2 < 60  GeV^2. The analysis is based on a data sample corresponding to an integrated luminosity of around 469  fb^(-1) collected at the PEP-II e^+e^− collider with the BABAR detector at center-of-mass energies near 10.6 GeV.