New results for K~+ → π`+ vv at low π~+ Momentum from BNL E949

摘要

The BNL E949 experiment was a successor to BNL E787 and was aimed to measure the branching ratio of the K~+→π~+vv decay. After detector upgrades were made, data equivalent to 1.7 x 10~(12) K~+ decays at rest were collected in a 2002 physics run. The data were analyzed via a blind analysis with a technique called the "Bifurcation Method". In this report we present the results of a search for K~+→ π+vv in the pion momentum region below K~+→π+π~0 peak. Three new candidate events were observed with an estimated background of 0.93 ± 0.17_(-0.24)~(+0.32) events. Combining these observation with previously reported results yields a branching ratio of BR(K~+→π~+vv) = (1.73_(1.05)~)+1.15x10~(-10) consistent with the standard model prediction.