Relativistic Corrections to $e^+e^- \to J/\psi + \eta_c$ in a Potential   Model
  We compute relativistic corrections to the process $e^+e^- \to J/\psi + \eta_c$ and find that they resolve the discrepancy between theory and experiment. 
Geoffrey T. Bodwin, Daekyoung Kang, Taewon Kim, Jungil Lee, Chaehyun   Yu