Rare kaon decays: Brookhaven E871

This paper describes recent results from the rare kaon decay Experiment 871 at the Brookhaven AGS, which searched for the lepton flavor violating decay KL0→μ±e±, and measured branching ratios for the GIM and helicity suppressed modes KL0→μ+μ- and KL0→e+e-. Observing no candidate μe events, E871 established a new upper limit (90%CL) on the branching fraction of B(KL0→μ±e±)<4.8x10-12, representing the most sensitive search to date for this decay mode. E871 measured over 6200 μμ candidates, a factor of six improvement on all previous measurements combined, giving a preliminary branching fraction of B(KL0→μ+μ-)=(7.23±0.22)x10-9, 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(KL0→e+e-)=8.7-4.1+5.7x10-12, which equals the smallest branching fraction ever measured in particle physics