SEMINAR      Wednesday 23 March 2005 - h. 15:00  Auditorium B. Touschek     A. Ceccucci  (CERN) Rare Kaon Decays: Opportunities at CERN Abstract     We have studied the possibility to measure the very rare decay K+ --> pi+ nu nubar at the CERN SPS. In our opinion a very competitive experiment capable of collecting about 100 events in two years of data taking can be done.     The experiment will employ a high energy, un-separated kaon beam in order to control backgrounds originating from the two pion kaon decays. The data taking may start before the end of this decade and lead to a ~10 % measurement of the CKM parameter Vtd.     The status of the project, including its technical challenges, and the prospects will be reviewed.