Measurements of D and Ds decay constants at CLEO

Meson decay constants in the B system are used to translate measurements of BB̄ mixing to CKMmatrix elements. Currently, it is not possible to determine fB accurately from leptonic B decays, so theoretical calculations of fB are used. Since the B s meson does not have l ν decays, it will never be possible to determine fBs experimentally, thus theory must be relied on. If calculations disagree on D mesons, they may be questionable on B mesons. If, on the other hand new physics is present, we need understand how it effects SM based predictions of the B decay constants. Decay constants can be calculated using lattice quantum-chromodynamics (LQCD). Recent calculation from Follana et al. using an unquenched LQCD predicts fD+ = (207± 4) MeV and fD+ s = (241± 3) MeV [2]. We use the reactions ee → DD, and ee → D∗− s D + s or D − s D ∗+ s . The D + is studied at 3770 MeV using 818 pb of data [3]. And the D s is studied at 4170 MeV, using 424 pb −1 for μν and τν, τ → πν̄, and 300 pb for τν, τ → eνν̄. (Eventually CLEO will present results using 600 pb.)