Measurement of the K^+　→　π^+ v v^^- branching ratio

概要

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Experiment E949 at Brookhaven National Laboratory studied the rare decay K^+ → π^+ vv^^- and otherprocesses with an exposure of 1.77 × 10^<12> K^+’s. The data were analyzed using a blind analysis techniqueyielding one candidate event with an estimated background of 0.30 ± 0.03 events. Combining this resultwith the observation of two candidate events by the predecessor experiment E787 gave the branching ratioB(K^+ → π^+ vv^^-)=(1.47^<+1.30>_<0.89>)×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 [V.V. Anisimovsky et al., Phys. Rev. Lett. 93, 031801 (2004)].