Latest Results from the Search for K+→π+νν¯

Brookhaven experiment E949 has continued the search for the rare decay K+→π+νν¯. The branching ratio for this second-order weak transition is an important test of the Standard Model; deviations from the predicted branching ratio of ∼0.8×10−10 could be indications of non-Standard Model physics. While the Standard Model prediction for the branching ratio has a small (∼ 7%) theoretical uncertainty, the experimental and analytical hurdles involved in making this measurement are formidable. This paper describes the key features of some of the techniques used in the measurement of B(K+→π+νν¯).