Measurement of the absolute branching fraction of Ds+→ τ+ντ decay

Using a sample of tagged D-s(+) decays collected near the (DsDs -/+)-D-*+/- peak production energy in e(+)e(-) collisions with the CLEO-c detector, we study the leptonic decay D-s(+)->tau(+)nu(tau) via the decay channel tau(+)-> e(+)nu(e)(nu) over bar (tau). We measure B(D-s(+)->tau(+)nu(tau))=(6.17 +/- 0.71 +/- 0.34)%, where the first error is statistical and the second systematic. Combining this result with our measurements of D-s(+)->mu(+)nu(mu) and D-s(+)->tau(+)nu(tau) (via tau(+)->pi(+)(nu) over bar (tau)), we determine f(Ds)=(274 +/- 10 +/- 5) MeV.