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Register a new userMeasurement of the CKM Matrix Element $|V_{cb}|$ from $B^{0} to D^{*-} ell^+ u_ell$ at Belle
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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.
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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.
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.
We report a measurement of the inclusive semileptonic $B_s^0$ branching fraction in a $121~fb^{-1}$ data sample collected near the $Upsilon(5S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider. Events containing $B_s^0$ pairs are selected by reconstructing a tag side $D_s^+$ and identifying a signal side lepton $ell^+$ ($ell = e, mu$) that is required to have the same-sign charge to ensure that both originate from different $B_s^0$ mesons. The $B_s^0 rightarrow X^- ell^+ u_ell$ branching fraction is extracted from the ratio of the measured yields of $D_s^+$ mesons and $D_s^+ ell^+$ pairs and the known production and branching fractions. The inclusive semileptonic branching fraction is measured to be $[9.6 pm 0.4text{(stat)} pm 0.7text{(syst)}]~%$.
We report measurements of the $bar{B}^0 to D^{*+} ell^{-} bar{ u}_l$ and $B^- to D^{0} ell^{-} bar{ u}_l$ processes using 34.6 fb$^{-1}$ of collision events recorded by the Belle II experiment at the SuperKEKB asymmetric-energy $e^+ e^-$ collider. For the $B^-to D^{0}ell^-bar u_ell$ channel, we present first studies that isolate this decay from other semileptonic processes and backgrounds. We report a measurement of the $bar{B}^0 to D^{*+} ell^{-} bar{ u}_l$ branching fraction and obtain ${cal B}(bar{B}^0 to D^{*+} ell^{-} bar{ u}_l) = left(4.60 pm 0.05_{mathrm{stat}}pm0.17_{mathrm{syst}} pm 0.45_{pi_s}right) %$, in agreement with the world average. Here, the uncertainties are statistical, systematic, and related to slow pion reconstruction, respectively. The systematic uncertainties are limited by the statistics of auxiliary measurements and will improve in the future. We also report differential branching fractions in five bins of the hadronic recoil parameter $w$ for $bar{B}^0 to D^{*+} ell^{-} bar{ u}_l$, unfolded to account for resolution and efficiency effects.
We extract $|V_{cb}|$ from the available data in the decay $B to D^{(*)}ell u_{ell}$. Our analysis uses the $q^2(w)$ binned differential decay rates in different subsamples of $Bto Dell u_ell$ ($ell = e, mu$), while for the decay $Bto D^*ell u_ell$, the unfolded binned differential decay rates of four kinematic variables including the $q^2$ bins have been used. In the CLN and BGL parameterizations of the form factors, the combined fit to all the available data along with their correlations yields $|V_{cb}| = (39.77 pm 0.89)times 10^{-3}$ and $(40.90 pm 0.94)times 10^{-3}$ respectively. In these fits, we have used the inputs from lattice and light cone sum rule (LCSR) along with the data. Using our fit results and the HQET relations (with the known corrections included) amongst the form factors, and parameterizing the unknown higher order corrections (in the ratios of HQET form factors) with a conservative estimate of the normalizing parameters, we obtain $R(D^{*}) = 0.259 pm 0.006$ (CLN) and $R(D^*) = 0.257 pm 0.005$ (BGL).
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