Measurement of B(Ds+→l+ν) and the decay constant fDs+ from 600pb-1 of e+e- annihilation data near 4170 MeV

We examine e + e - → D - s D* + s and D* - s D + s interactions at 4170 MeV using the CLEO-c detector in order to measure the decay constant f D+s with good precision. Previously our measurements were substantially higher than the most precise lattice based QCD calculation of (241 ± 3) MeV. Here we use the D + s → l + v channel, where the l + designates either a μ + or a τ + , when the τ + → π + P. Analyzing both modes independently, we determine B(D + s → μ + v) = (0.565 ± 0.045 ± 0.017)%, and B(D + s → τ + v) = (6.42 ± 0.81 ± 0.18)%. We also analyze them simultaneously to find an effective value of B eff (D + s → μ + v) = (0.591 ± 0.037 ± 0.018)% and f D+s = (263.3 ± 8.2 ± 3.9) MeV. Combining with the CLEO-c value determined independently using D + s → τ + v, τ + → e + vV decays, we extract f D+s = (259.5 ± 6.6 ± 3.1) MeV. Combining with our previous determination of Β(D + → μ + v), we extract the ratio f D+s /f D+ = 1.26 ± 0.06 ± 0.02. No evidence is found for a CP asymmetry between T(D + s → μ + v) and Γ(D - s → μ - v); specifically the fractional difference in rates is measured to be (4.8 ± 6.1)%. Finally, we find B(D + s → e + v) < 1.2 X 10 -4 at 90% confidence level.