Measurement of the Pseudoscalar Decay Constant fDs Using Charm-Tagged Events in e+e− Collisions at √s=10.58 GeV

Abstract

Using 230.2 fb − 1 of e + e − annihilation data collected with the BABAR detector at and near the peak of the Υ ( 4 S ) resonance, 489 ± 55 events containing the pure leptonic decay D + s → μ + ν μ have been isolated in charm-tagged events. The ratio of partial widths Γ ( D + s → μ + ν μ ) / Γ ( D + s → ϕ π + ) is measured to be 0.143 ± 0.018 ± 0.006 allowing a determination of the pseudoscalar decay constant f D s = ( 283 ± 17 ± 7 ± 14 ) MeV . The errors are statistical, systematic, and from the D + s → ϕ π + branching ratio, respectively.