Phys. Rev. Lett. 83, 922–925 (1999)Measurement of the Branching Ratio of π0 → e+e- Using KL → 3π0 Decays in FlightReceived 10 March 1999; published in the issue dated 2 August 1999 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. © 1999 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.83.922
DOI:
10.1103/PhysRevLett.83.922
PACS:
13.20.Cz, 13.40.Gp, 13.40.Hq
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