A Measurement of the Branching Ratio of $K_L \to e^+e^-\gamma\gamma$
  We report on a study of the decay $K_L \to e^+e^-\gamma\gamma$ carried out as a part of the KTeV/E799 experiment at Fermilab. The 1997 data yielded a sample of 1543 events, including an expected background of $56 \pm 8$ events. An effective form factor was determined from the observed distribution of the $e^+e^-$ invariant mass. Using this form factor in the calculation of the detector acceptance, the branching ratio was measured to be ${\mathcal B}(K_L \to e^+ e^- \gamma \gamma, E^*_\gamma > 5 {MeV}) = (5.84 \pm 0.15 {\rm ~(stat)} \pm 0.32 {\rm ~(sys)})\times 10^{-7}$. 
The KTeV Collaboration, A. Alavi-Harati, et al