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Register a new userMeasurement of the form factors of the decay B^0 -> D^{*-} l^+ nu_l and determination of the CKM matrix element |V_{cb}|
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This paper describes a determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ using the decay $B^0to D^{*-}ell^+ u_ell$. We perform a combined measurement of this quantity and of the form factors $rho^2$, $R_1(1)$, and $R_2(1)$ which fully characterize this decay in the framework of heavy-quark effective theory, based on 140 fb$^{-1}$ of Belle data collected near the $Upsilon(4S)$ resonance. The results, based on about 69,000 reconstructed $B^0to D^{*-}ell^+ u_ell$ decays, are $rho^2=1.293pm 0.045pm 0.029$, $R_1(1)=1.495pm 0.050pm 0.062$, $R_2(1)=0.844pm 0.034pm 0.019$ and $mathcal{F}(1)|V_{cb}|=34.4pm 0.2pm 1.0$. The $B^0to D^{*-}ell^+ u_ell$ branching fraction is found to be $(4.42pm 0.03pm 0.25)%$. For all these numbers, the first error is the statistical and the second is the systematic uncertainty. All results are preliminary.
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We present a new measurement of the CKM matrix element $|V_{cb}|$ from $B^{0} to D^{*-} ell^+ u_ell$ decays, reconstructed with the full Belle data set of $711 , rm fb^{-1}$ integrated luminosity. Two form factor parameterizations, originally conceived by the Caprini-Lellouch-Neubert (CLN) and the Boyd, Grinstein and Lebed (BGL) groups, are used to extract the product $mathcal{F}(1)eta_{rm EW}|V_{cb}|$ and the decay form factors, where $mathcal{F}(1)$ is the normalization factor and $eta_{rm EW}$ is a small electroweak correction. In the CLN parameterization we find $mathcal{F}(1)eta_{rm EW}|V_{cb}| = (35.06 pm 0.15 pm 0.56) times 10^{-3}$, $rho^{2}=1.106 pm 0.031 pm 0.007$, $R_{1}(1)=1.229 pm 0.028 pm 0.009$, $R_{2}(1)=0.852 pm 0.021 pm 0.006$. For the BGL parameterization we obtain $mathcal{F}(1)eta_{rm EW}|V_{cb}|= (34.93 pm 0.23 pm 0.59)times 10^{-3}$, which is consistent with the World Average when correcting for $mathcal{F}(1)eta_{rm EW}$. The branching fraction of $B^{0} to D^{*-} ell^+ u_ell$ is measured to be $mathcal{B}(B^{0}rightarrow D^{*-}ell^{+} u_{ell}) = (4.90 pm 0.02 pm 0.16)%$. We also present a new test of lepton flavor universality violation in semileptonic $B$ decays, $frac{{cal B }(B^0 to D^{*-} e^+ u)}{{cal B }(B^0 to D^{*-} mu^+ u)} = 1.01 pm 0.01 pm 0.03~$. The errors correspond to the statistical and systematic uncertainties respectively. This is the most precise measurement of $mathcal{F}(1)eta_{rm EW}|V_{cb}|$ and form factors to date and the first experimental study of the BGL form factor parameterization in an experimental measurement.
We determine the CKM matrix element |Vcb| using a sample of 3.33 million BBbar events in the CLEO detector at CESR. We determine the yield of reconstructed B --> D*+ l nu decays as a function of w = v_B . v_D*, and from this we obtain the differential decay rate dGamma/dw. By extrapolating the differential decay rate to w=1, the kinematic point at which the D* is at rest relative to the B, we extract the product |Vcb| F(1), where F(1) is the form factor at w=1 and is predicted accurately by theory. We find |Vcb| F(1) = 0.0424 +- 0.0018(stat.) +- 0.0019(syst.). We also integrate the differential decay rate over w to obtain B(B --> D*+ l nu) = (5.66 +- 0.29 +- 0.33)%. All results are preliminary.
This article describes a determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ from the decay $B^0to D^{*-}ell^+ u_ell$ using 711 fb$^{-1}$ of Belle data collected near the $Upsilon(4S)$ resonance. We simultaneously measure the product of the form factor normalization $mathcal{F}(1)$ and the matrix element $|V_{cb}|$ as well as the three parameters $rho^2$, $R_1(1)$ and $R_2(1)$, which determine the form factors of this decay in the framework of the Heavy Quark Effective Theory. The results, based on about 120,000 reconstructed $B^0to D^{*-}ell^+ u_ell$ decays, are $rho^2=1.214pm 0.034pm 0.009$, $R_1(1)=1.401pm 0.034pm 0.018$, $R_2(1)=0.864pm 0.024pm 0.008$ and $mathcal{F}(1)|V_{cb}|=(34.6pm 0.2pm 1.0)times 10^{-3}$. The branching fraction of $B^0to D^{*-}ell^+ u_ell$ is measured at the same time; we obtain a value of $mathcal{B}(B^0 to D^{*-}ell^+ u_ell) = (4.58 pm 0.03 pm 0.26) %$. The errors correspond to the statistical and systematic uncertainties. These results give the most precise determination of the form factor parameters and $mathcal{F}(1)|V_{cb}|$ to date. In addition, a direct, model-independent determination of the form factor shapes has been carried out.
The precise determination of the CKM matrix element $left| V_{cb}right|$ is important for carrying out tests of the flavour sector of the Standard Model. In this article we present a preliminary analysis of the $bar B^0 to D^{*,+} , ell^- , bar u_ell$ decay mode and its charge conjugate, selected in events that contain a fully reconstructed $B$-meson, using 772 million $e^+ , e^- to Upsilon(4S) to B bar B$ events recorded by the Belle detector at KEKB. Unfolded differential decay rates of four kinematic variables fully describing the $bar B^0 to D^{*,+} , ell^- , bar u_ell$ decay in the $B$-meson rest frame are presented. We measure the total branching fraction $mathcal{B}( bar B^0 to D^{*,+} , ell^- , bar u_ell ) = left(4.95 pm 0.11 pm 0.22 right) times 10^{-2}$, where the errors are statistical and systematic respectively. The value of $left|V_{cb} right|$ is determined to be $left( 37.4 pm 1.3 right) times 10^{-3}$. Both results are in good agreement with current world averages.
I discuss recent progress in lattice calculations of $B to D^{(*)} ell u$ form factors, important for the precision determination of $|V_{cb}|$ in the Standard Model (SM), and for testing SM expectations of lepton flavor universality in observables $R(D^{(*)})$. I also discuss progress in calculations of the related $b to c$ semileptonic decays $B_s to D_s^{(*)} ell u$ and $B_c to J/psi , ell u$ now experimentally accessible at the LHC.
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