Measurement of the branching ratio of pi^0 -> e^+e^- using K_L -> 3 pi^0 decays in flight

Abstract

The branching ratio of the rare decay pi^0 -> e^+e^- has been measured in E799-II, a rare kaon decay experiment using the KTeV detector at Fermilab. The pi^0's were produced in fully-reconstructed K_L -> 3 pi^0 decays in flight. We observed 275 candidate pi^0 -> e^+e^- events, with an expected background of 21.4 +- 6.2 events which includes the contribution from Dalitz decays. We measured BR(pi^0 -> e^+e^-, x>0.95) = (6.09 +- 0.40 +- 0.24) times 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.

New version shortened to PRL length limit. 5 pages, 4 figures. Published in Phys. Rev. Lett

References in corpus (2)

• Long-distance contributions to the K_L --> mu+ mu- decay width
• Long Distance Contribution to $K_L\to {\ell }^{+}{\ell }^{-}$

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• Measurements of the Decay KL->e+e-mu+mu-
• Search for direct production of a2(1320) and f2(1270) mesons in e+e- annihilation
• Measurements of the Decay $K_L\to e^{+}{e}^{-}\gamma$
• Branching Ratio Measurement of the decay K_L -> e+ e- mu+ mu-
• Observation of the Decay $K_L\to {\mu }^{+}{\mu }^{-}\gamma \gamma$
• Neutral-pion decay into an electron-positron pair: A review and update