Measurement of the CKM matrix element |Vcb | from B0 →d∗-ℓ+νℓ at Belle

Abstract

We present a new measurement of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| from B0→D∗-ℓ+νℓ 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)ηEW|Vcb| and the decay form factors, where F(1) is the normalization factor and ηEW is a small electroweak correction. In the CLN parametrization we find F(1)ηEW|Vcb|=(35.06±0.15±0.56)×10-3, ρ2=1.106±0.031±0.007, R1(1)=1.229±0.028±0.009, R2(1)=0.852±0.021±0.006. For the BGL parametrization we obtain F(1)ηEW|Vcb|=(34.93±0.23±0.59)×10-3, which is consistent with the world average when correcting for F(1)ηEW. The branching fraction of B0→D∗-ℓ+νℓ is measured to be B(B0→D∗-ℓ+νℓ)=(4.90±0.02±0.16)%. We also present a new test of lepton flavor universality violation in semileptonic B decays, B(B0→D∗-e+ν)B(B0→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)ηEW|Vcb| and form factors to date and the first experimental study of the BGL form factor parametrization in an experimental measurement.