Improved measurement of absolute branching fraction of Ds+→τ+ν τ

We have studied the leptonic decay D + s → τ + v τ , via the decay channel τ + → e + v e v τ , using a sample of tagged D + s decays collected near the D* ± s D ∓ s peak production energy in e + e - collisions with the CLEO-c detector. We obtain B(D + s → τ + v τ ) = (5.30 ± 0.47 ± 0.22)% and determine the decay constant f Ds = (252.5 ± 11.1 ± 5.2) MeV, where the first uncertainties are statistical and the second are systematic.