Measurements of the branching fractions of the semileptonic decays and the asymmetry parameter of

Li, Y. B.*; Tanida, Kiyoshi   ; Belle Collaboration*; 182 of others*

Using data samples of 89.5 and 711 fb recorded at energies of and GeV, respectively, with the Belle detector at the KEKB collider, we report measurements of branching fractions of semileptonic decays ( or ) and the -asymmetry parameter of decay. The branching fractions are measured to be )=()% and )=()%, and the decay parameter is measured to be with much improved precision compared to the current world average. The corresponding ratio / is 1.03 0.05 0.07, which is consistent with the expectation of lepton flavor universality. The first measured asymmetry parameter is found to be consistent with zero. The first and the second uncertainties above are statistical and systematic, respectively, while the third ones arise due to the uncertainty of the branching fraction.