Measurement of the Absolute Branching Fraction of Ds+ →τ+ντ via τ+ →e+νe ν ¯ τ

Abstract

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 Ds+→τ+ντ via τ+→e+νeν¯τ, and find BDs+→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 fDs+ from lattice quantum chromodynamics calculations or the |Vcs| from the CKMfitter group, we extract |Vcs|=0.978±0.009±0.012 and fDs+=(251.1±2.4±3.0) MeV, respectively. Combining our result with the world averages of BDs+→τ+ντ and BDs+→μ+νμ, we obtain the ratio of the branching fractions BDs+→τ+ντ/BDs+→μ+νμ=9.72±0.37, which is consistent with the standard model prediction of lepton flavor universality.