First Observation of the Rare Decay Mode K-long -> e+ e-

Abstract

In an experiment designed to search for and study very rare two-body decay modes of the K-long, we have observed four examples of the decay K-long -> e+ e-, where the expected background is 0.17+-0.10 events. This observation translates into a branching fraction of 8.7^{+5.7}_{-4.1} X 10^{-12}, consistent with recent theoretical predictions. This result represents by far the smallest branching fraction yet measured in particle physics.

9 pages, 3 figures

References in corpus (3)

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

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