We study the reaction e+e-→e+e -ηc, ηc→KSK±π" and obtain ηc mass and width values 2982.2±0.4±1.6MeV/c2 and 31.7±1.2±0.8MeV, respectively. We find Γ(ηc→γ γ)B(ηc→KK̄π)=0.374±0.009±0.031keV, and measure the γγ*→ηc transition form factor in the momentum transfer range from 2 to 50GeV2. The analysis is based on 469fb-1 of integrated luminosity collected at PEP-II with the BABAR detector at e+e- center-of-mass energies near 10.6 GeV.
Lees, J., Poireau, V., Prencipe, E., Tisserand, V., Tico, J., Grauges, E., et al. (2010). Measurement of the γγ*→ηc transition form factor. PHYSICAL REVIEW D, PARTICLES, FIELDS, GRAVITATION, AND COSMOLOGY, 81(5) [10.1103/PhysRevD.81.052010].