The branching ratio of the rare decay π0 → e+e- has been measured in E799-II, a rare kaon decay experiment using the KTeV detector at Fermilab. We observed 275 candidate π0 → e+e- events, with an expected background of 21.4 ± 6.2 events which includes the contribution from Dalitz decays. We measured B[π0 → e+e-,(me+e-/mπ0)2 > 0.95] = (6.09 ± 0.40 ± 0.24) × 10-8, where the first error is statistical and the second systematic. This result is the first significant observation of the excess rate for this decay above the unitarity lower bound.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)