The rare kaon decay K+ -> pi+ nu nubar is very sensitive to the
  coupling of top to down quarks, V_{td}, in the Cabibbo-Kobayashi
  -Maskawa quark mixing matrix. In the Standard Model of particle
  physics,the predicted branching ratio is 0.75 +- 0.29 E-10.
  The E787 experiment at the Alternating Gradient Synchrotron of
  Brookhaven National Laboratory (BNL) in the US is a rare kaon-
  decay experiment studying K+ -> pi+ nu nubar and related decays,
  using kaon decays at rest. In the data samples from 1995 to 1997,
  a single event consistent with the decay K+ -> pi+ nu nubar at a
  branching ratio of 1.5 E-10 was found [PRL 84, 3768 (2000), 79,
  2204 (1997)].


  In this seminar, final results on K+ -> pi+ nu nubar from E787
  are presented, including a new 1998 data sample of comparable
  sensitivity to that reported previously. E787's results on other
  kaon decays and the prospects in an upgraded version of the
  experiment, BNL-E949, are also discussed.