Measurement of the Absolute Branching Fraction of D+s→τ+ντ via τ+ → e+νe¯ντ

Using a dataset of 6.32 fb−1 of e+e− annihilation data collected with the BESIII detector at center-of-mass energies between 4178 and 4226 MeV, we have measured the absolute branching fraction of the leptonic decay D+s→τ+ντ via τ+→e+νe¯ντ, and find BD+s→τ+ντ = (5.27±0.10±0.12)×10−2, where the first uncertainty is statistical and the second is systematic. The precision is improved by a factor of 2 compared to the previous best measurement. Combining with fD+s from lattice quantum chromodynamics calculations or the |Vcs| from the CKMfitter group, we extract |Vcs|=0.978±0.009±0.012 and fD+s = (251.1±2.4±3.0) MeV, respectively. Combining our result with the world averages of BD+s→τ+ντ and BD+s→μ+νμ, we obtain the ratio of the branching fractions BD+s→τ+ντ/BD+s→μ+νμ = 9.72±0.37, which is consistent with the standard model prediction of lepton flavor universality. For complete list of authors see http://dx.doi.org/10.1103/PhysRevLett.127.171801