Measurement of the branching ratio of KL→e+e-γγ

We report on a study of the decay K{sub L}{r_arrow}e{sup +}e{sup {minus}}{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{+-}8 events. An effective form factor was determined from the observed distribution of the e{sup +}e{sup {minus}} invariant mass. Using this form factor in the calculation of the detector acceptance, the branching ratio was measured to be B(K{sub L}{r_arrow}e{sup +}e{sup {minus}}{gamma}{gamma},E{sub {gamma}}{sup *}{gt}5MeV)=(5.84{+-}0.15(stat){+-}0.32(syst)){times}10{sup {minus}7}.