Determination of theB¯→D*lν¯decay width and|Vcb|

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Abstract

In the standard model, the charged current of the weak interaction is governed by a unitary quark mixing matrix that also leads to CP violation. Measurement of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements is essential to searches for new physics, either through the structure of the CKM matrix, or a departure from unitarity. We determine the CKM matrix element $|{V}_{\mathrm{cb}}|$ using a sample of $3\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $B\overline{B}$ events in the CLEO detector at the Cornell Electron Storage Ring. We determine the yield of reconstructed ${B}^{0}\ensuremath{\rightarrow}{D}^{*+}\mathcal{l}\overline{\ensuremath{\nu}}$ and ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{D}^{*0}\mathcal{l}\overline{\ensuremath{\nu}}$ decays as a function of w, the boost of the ${D}^{*}$ in the B rest frame, and from this we obtain the differential decay rate $d\ensuremath{\Gamma}/dw.$ By extrapolating $d\ensuremath{\Gamma}/dw$ to $w=1,$ the kinematic end point at which the ${D}^{*}$ is at rest relative to the B, we extract the product $|{V}_{\mathrm{cb}}|\mathcal{F}(1),$ where $\mathcal{F}(1)$ is the form factor at $w=1.$ We find $|{V}_{\mathrm{cb}}|\mathcal{F}(1)=0.0431\ifmmode\pm\else\textpm\fi{}0.0013(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.0018(\mathrm{syst}).$ We combine $|{V}_{\mathrm{cb}}|\mathcal{F}(1)$ with theoretical results for $\mathcal{F}(1)$ to determine $|{V}_{\mathrm{cb}}|=0.0469\ifmmode\pm\else\textpm\fi{}0.0014(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.0020(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.0018(\mathrm{theor}).$ We also integrate the differential decay rate over w to obtain $\mathcal{B}({B}^{0}\ensuremath{\rightarrow}{D}^{*+}\mathcal{l}\overline{\ensuremath{\nu}})=(6.09\ifmmode\pm\else\textpm\fi{}0.19\ifmmode\pm\else\textpm\fi{}0.40)%$ and $\mathcal{B}{(B}^{\ensuremath{-}}\ensuremath{\rightarrow}{D}^{*0}\mathcal{l}\overline{\ensuremath{\nu}})=(6.50\ifmmode\pm\else\textpm\fi{}0.20\ifmmode\pm\else\textpm\fi{}0.43)%.$

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