Measurements of D and Ds decay constants at CLEO

Abstract

Using CLEO data collected at 3370 MeV and 4170 MeV, we determine fD = (205.8 +- 8.5 +- 2.5) MeV and an interim preliminary value of fDs = (267.9 +- 8.2 +- 3.9) MeV, where both results are radiatively corrected. They agree with the recent most precise unquenched Lattice-QCD calculation for the D+, but do not for the Ds. Several consequences are discussed.