We propose to measure the very rare kaon decay K+-> pi+ nu nubar at the CERN SPS to extract a 10% measurement of the
CKM parameter |Vtd|.
The proposed experiment aims to collect about 80 K+-> pi+ nu nubar events at the SM prediction with a signal to background ratio
of 10:1 in two years of data taking.
We propose to use 400 GeV/c protons from the SPS to perform the experiment.
The are several challenging aspects for this experiment. They include: