Measurement of the K+→π+νν̄ branching ratio

Abstract

Experiment E949 at Brookhaven National Laboratory studied the rare decay K+→π+νν̄ and other processes with an exposure of 1.77×1012 K+'s. The data were analyzed using a blind analysis technique yielding one candidate event with an estimated background of 0.30±0.03 events. Combining this result with the observation of two candidate events by the predecessor experiment E787 gave the branching ratio B(K+→π+νν ̄)=(1.47-0.89+1.30)×10-10, consistent with the standard model prediction of (0.74±0.20)×10-10. This is a more detailed report of results previously published. © 2008 The American Physical Society.