| A precise branching ratio measurement of the rare decay pi0 → e+e - has been made. The measurement was made with the rare kaon decay experiment KTeV at Fermilab where the source of pi0s was KL → pi0pi 0pi0 decaying in flight. A total of 794 fully reconstructed KL → 3pi0 events consistent with two of the intermediate pi0s decaying into gammagamma and one into e+e- were collected. An estimated 53.2 +/- 11.0 of these events were expected to be background. Normalizing to the pi0 Dalitz decay we found Br&parl0;p 0→e+e-, me+e-mp 02>0 .95&parr0;=6.44+/-0.25st at+/-0.22sys x10 -81 where internal radiation, pi0 → e+e-(gamma), was limited by the requirement ( me+e- /mpi0)2 > 0.95 which separated it from the tree level Dalitz decay, pi0 → e+e-gamma. |
