Determination of |V_cb| from the semileptonic decay B⁰ → D*⁻ℓ⁺ ν

Abstract

Semileptonic decays B→ D*⁻ ℓ ⁺ νX were selected from a sample of 3.1 million hadronic Z decays collected by the DELPHI detector at LEP. A topological search for semileptonic B decays to resonant and non-resonant D*⁻ π ⁺ states was performed and the ratio of the branching fractions:

$$\frac{{Br(B \to D^* \ell ^ + X)}}{\begin{gathered} Br(B \to D^* \ell ^ + vX) + Br(B^0 \to D^{* - } \ell ^ + v) \hfill \\ = 0.19 \pm 0.10(stat) \pm 0.06(syst) \hfill \\ \end{gathered} }$$

was determined. Taking into account this contribution, the differential decay width of B⁰→D*⁻ℓ⁺ ℓ ⁺ ν was measured as a function of the momentum transfer from the B to the D*⁻ in two separate analyses, using exclusive and inclusive methods of D*⁻ reconstruction. The distributions were fitted over the full momentum transfer range to extract the product of |V_cb| times the normalization of the decay form factorF(q ²_max ):

$$F(q_{max}^2 )|V_{cb} | = (35.4 + 1.9(stat) \pm 2.4(syst)) \cdot 10^{ - 3} $$

. The value of |V_cb| was computed using theoretical calculations ofF( q ²_max ), giving:

$$|V_{cb} | = (39.9 \pm 2.0(stat) \pm 2.6(syst) \pm 1.7(theory)) \cdot 10^{ - 3} $$

. The total branching fractionBr(B ⁰→D*⁻ ℓ ⁺ gn) was determined to be:

$$Br(B^0 \to D^{* - } \ell ^ + v) = (5.52 \pm 0.17(stat) \pm 0.68(syst))\% $$

.