Determination of pseudoscalar-charmed-meson decay constants from B-meson decays

Recent progress in understanding form factors for weak B→D and B→D* transitions, combined with a factorization hypothesis, allows one to extract the pseudoscalar-meson decay constant fDs=259±74 MeV, implying that the branching ratios for Ds→τ bar ντ and Ds→μ bar νμ are (4.6±2.6)% and (0.5±0.3)%, respectively. A scaling law for nonrelativistic wave functions then implies fD=207±60 MeV, fB=140±40 MeV, and fBs=175±50 MeV. Other consequences of the approach include a prediction that the branching ratio of bar B 0 to D*+D*- is about 0.06%, of which 94% occurs in the CP=+ final state