Measurement of Rare Kaon Decay K^+ -> PI^+NUNU-BAR
  A decade long search for the rare kaon decay to pi^+nunu-bar has been pursued by E787. Two signal events are observed, giving a measurement of the branching ratio Br(K^+ -> PI^+NUNU-BAR)=1.57^+1.75_-0.82 x 10^-10 and a constraint on the Cabibbo-Kobayashi-Maskawa (CKM) matrix element 0.007<|Vtd|<0.030 (68% C.L.). 
Shaomin Chen