Measurement of |Vcb| using the semileptonic decay B d0 → D*+ℓ-ν ℓ

Data from Z decays in DELPHI have been searched for Bd0 → D*+ℓ-νℓ with the D*+ decaying to D0π+ and D0 → K-π+, K-π +π+π- or K-π +(π0). These events are used to measure the CKM matrix element |Vcb| and the form factor slope, ρA12: ℱD* (1) |Vcb| = 0.0392 ± 0.0018 ± 0.0023; ρA12 = 1.32 ± 0.15 ± 0.33 corresponding to a branching fraction: BR(Bd0 → D*+ℓ-νℓ) = (5.90 ± 0.22 ± 0.50)%. Combining these and previous DELPHI measurements gives: ℱD* (1) |Vcb| = 0.0377 ± 0.0011 ± 0.0019, ρA12 = 1.39 ± 0.10 ± 0.33 and BR(Bd0 → D* +ℓ-νℓ) = (5.39 ± 0.11 ± 0.34)% Using ℱD* (1) = 0.91 ± 0.04, yields: |Vcbl = 0.0414 ± 0.0012(stat.) ± 0.0021(syst.) ± 0.0018(theory). The b-quark semileptonic branching fraction into a D*+ emitted from higher mass charmed excited states has also been measured to be: BR(b → D*+Xℓ-ν ℓ) = (0.67 ± 0.08 ± 0.10)%.