Rare kaon decays: Brookhaven E871

This paper describes recent results from the rare kaon decay Experiment 871 at the Brookhaveen AGS, which searched for the lepton flavor violating decay K-L(0) --> mu(+/-)e(-/+), and measured branching ratios for the GIM and helicity suppressed modes K-L(0) --> mu(+)mu(-) and K-L(0) --> e(+)e(-). Observing no candidate mu e events, E871 established a new upper limit (90% CL) on the branching fraction of B(K-L(0) --> mu(+/-)e(-/+)) < 4.8 x 10(-12), representing the most sensitive search to date for this mode. E871 measured over 6200 mu mu candidates, a factor of six improvement on all previous measurements combined, giving a preliminary branching fraction of B(K-L(0) --> mu(+)mu(-)) = (7.23 +/- 0.22) x 10(-9), which should reduce the uncertainty in this decay mode by a factor of three. Lastly, E871 recorded four candidate ee events, the first observation of this rare decay, leading to a branching fraction of B(K-L(0)--> e(+)e(-)) = 8.7(-4.1)(+5.7) x 10(-12), which equals the smallest branching fraction ever measured in particle physics.