Measurement of the Absolute Branching Fraction of Ds+ ? ?+?? via ?+ ? e+?e(?)over-bar?

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 D-s(+) -> tau(+)nu(tau) via tau(+) -> e(+)nu(e)(nu) over bar (tau), and find B-Ds+(->tau+nu tau) = (5.27 +/- 0.10 +/- 0.12) x 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 f(Ds+) from lattice quantum chromodynamics calculations or the vertical bar V-cs vertical bar from the CKMfitter group, we extract vertical bar V-cs vertical bar = 0.978 +/- 0.009 +/- 0.012 and f(Ds+) = (251.1 +/- 2.4 +/- 3.0) MeV, respectively. Combining our result with the world averages of BDs+->tau+nu tau and BDs+->mu+nu mu, we obtain the ratio of the branching fractions BDs+->tau+nu tau/BDs+->mu+nu mu = 9.72 +/- 0.37, which is consistent with the standard model prediction of lepton flavor universality.