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Measurement of the absolute branching fractions for Ds-→ℓ-ν¯ℓ and extraction of the decay constant fDs


The absolute branching fractions for the decays Ds-→ℓ -ν̄ℓ (ℓ=e, μ, or τ) are measured using a data sample corresponding to an integrated luminosity of 521fb -1 collected at center-of-mass energies near 10.58 GeV with the BABAR detector at the PEP-II e+e- collider at SLAC. The number of Ds- mesons is determined by reconstructing the recoiling system DKXγ in events of the type e+e-→DKXDs*-, where Ds*-→Ds-γ and X represents additional pions from fragmentation. The Ds-→ℓ-νℓ events are detected by full or partial reconstruction of the recoiling system DKXγℓ. The branching fraction measurements are combined to determine the Ds- decay constant fD s=(258.6±6.4±7.5)MeV, where the first uncertainty is statistical and the second is systematic. © 2010 The American Physical Society.

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