Measurement of the branching fraction of leptonic decay Ds+ ? ?+?? via ?+ ? ?+?0<(?)over bar>?

Abstract

By analyzing 6.32 fb(-1) of e(+)e(-) annihilation data collected at the center-of-mass energies between 4.178 and 4.226 GeV with the BESIII detector, we determine the branching fraction of the leptonic decay D-s(+) -> tau(+)nu(tau), with tau(+) -> pi(+)pi(0)(nu) over bar (tau), to be BDs+->nu tau = (5.29 +/- 0.25(stat) +/- 0.20(syst))%. We estimate the product of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cs vertical bar and the D-s(+) decay constant to be f(Ds+1) to be f(Ds+) vertical bar V-cs vertical bar = (244.8 +/- 5.8(stat) +/- 4.8(syst)) MeV, using the known values of the tau(+) and D-s(+) masses as well as the D-s(+) lifetime, together with our branching fraction measurement. Combining the value of vertical bar V-cs vertical bar obtained from a global fit in the standard model and fm from lattice quantum chromodynamics, we obtain f(Ds+) = (251.6 +/- 5.9(stat) +/- 4.9(syst)) MeV and vertical bar V-cs vertical bar = 0.980 +/- 0.023(stat) +/- 0.019(syst). Using the branching fraction of BDs+->mu+nu mu = (5.35 +/- 0.21) x 10(-3), we obtain the ratio of the branching fractions BDs+->tau+nu tau/BDs+->mu+nu mu = 9.89 +/- 0.71, which is consistent with the standard model prediction of lepton flavor universality.