Measurement of the CKM matrix element |V_(cb)| from B~0 → D~(*-)?~+ ν_? at Belle

摘要

We present a new measurement of the Cabibbo-Kobayashi-Maskawa matrix element |V_(cb)| from B~0 → D~(*-)?~+ ν_? decays, reconstructed with the full Belle data set of 711 fb~(-1) integrated luminosity. Two form factor parametrizations, originally conceived by the Caprini-Lellouch-Neubert (CLN) and the Boyd,Grinstein and Lebed (BGL) groups, are used to extract the product F(1)η_(EW)|V_(cb)| and the decay form factors, where F(1) is the normalization factor and η_(EW) is a small electroweak correction. In the CLN parametrization we find F(1)η_(EW)|V_(cb)| = (35.06 ± 0.15 ± 0.56) × 10-3, ρ~2 = 1.106 ± 0.031 ± 0.007,R_1(1) = 1.229 ± 0.028 ± 0.009, R_2(1) = 0.852 ± 0.021 ± 0.006. For the BGL parametrization we obtain F(1)η_(EW)|V_(cb)| = (34.93 ± 0.23 ± 0.59) × 10~(-3), which is consistent with the world average when correcting for F(1)η_(EW). The branching fraction of B~0 → D~(*-)?~+ ν_? is measured to be B(B~0 → D~(*-)?~+ ν_?) = (4.90 ± 0.02 ± 0.16)%. We also present a new test of lepton flavor universality violation in semileptonic B decays, B(B~0→D~(*-)e~+ν)/B(B~0→D~(*-)μ~+ν) = 1.01 ± 0.01 ± 0.03. The errors quoted correspond to the statistical and systematic uncertainties, respectively. This is the most precise measurement of F(1)η_(EW)|V_(cb)| and form factors to date and the first experimental study of the BGL form factor parametrization in an experimental measurement.