Measurement of the B¯0→D*+ℓ−ν¯ℓ decay rate and |Vcb|

Le résumé fourni par la source

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element $|{V}_{cb}|$ based on a sample of about 53 700 ${\overline{B}}^{0}\ensuremath{\rightarrow}{D}^{*+}{\ensuremath{\ell}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ decays observed by the BABAR detector. We obtain the branching fraction averaged over $\ensuremath{\ell}=e,\ensuremath{\mu}$, $\mathcal{B}({\overline{B}}^{0}\ensuremath{\rightarrow}{D}^{*+}{\ensuremath{\ell}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}})=\mathbf{(}4.90\ifmmode\pm\else\textpm\fi{}0.07{(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}.)}_{\ensuremath{-}0.35}^{+0.36}(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}.)\mathbf{)}%$. We measure the differential decay rate as a function of $w$, the relativistic boost $\ensuremath{\gamma}$ of the ${D}^{*+}$ in the ${\overline{B}}^{0}$ rest frame. By extrapolating $d\ensuremath{\Gamma}/dw$ to the kinematic limit $w\ensuremath{\rightarrow}1$, we extract the product of $|{V}_{cb}|$ and the axial form factor ${\mathcal{A}}_{1}(w=1)$. We combine this measurement with a lattice QCD calculation of ${\mathcal{A}}_{1}(w=1)$ to determine $|{V}_{cb}|=\mathbf{(}38.7\ifmmode\pm\else\textpm\fi{}0.3(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}.)\ifmmode\pm\else\textpm\fi{}1.7{(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}.)}_{\ensuremath{-}1.3}^{+1.5}(\mathrm{\text{theory}})\mathbf{)}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}.$

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