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Register a new userBranching fraction and form-factor shape measurements of exclusive charmless semileptonic B decays, and determination of |V_{ub}|
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We report the results of a study of the exclusive charmless semileptonic decays, B^0 --> pi^- l^+ nu, B^+ --> pi^0 l^+ nu, B^+ --> omega l^+ nu, B^+ --> eta l^+ nu and B^+ --> eta^ l^+ nu, (l = e or mu) undertaken with approximately 462x10^6 Bbar{B} pairs collected at the Upsilon(4S) resonance with the BABAR detector. The analysis uses events in which the signal B decays are reconstructed with a loose neutrino reconstruction technique. We obtain partial branching fractions in several bins of q^2, the square of the momentum transferred to the lepton-neutrino pair, for B^0 --> pi^- l^+ nu, B^+ --> pi^0 l^+ nu, B^+ --> omega l^+ nu and B^+ --> eta l^+ nu. From these distributions, we extract the form-factor shapes f_+(q^2) and the total branching fractions BF(B^0 --> pi^- l^+ nu) = (1.45 +/- 0.04_{stat} +/- 0.06_{syst})x10^-4 (combined pi^- and pi^0 decay channels assuming isospin symmetry), BF(B^+ --> omega l^+ nu) = (1.19 +/- 0.16_{stat} +/- 0.09_{syst})x10^-4 and BF(B^+ --> eta l^+ nu) = (0.38 +/- 0.05_{stat} +/- 0.05_{syst})x10^-4. We also measure BF(B^+ --> eta^ l^+ nu) = (0.24 +/- 0.08_{stat} +/- 0.03_{syst})x10^-4. We obtain values for the magnitude of the CKM matrix element V_{ub} by direct comparison with three different QCD calculations in restricted q^2 ranges of B --> pi l^+ nu decays. From a simultaneous fit to the experimental data over the full q^2 range and the FNAL/MILC lattice QCD predictions, we obtain |V_{ub}| = (3.25 +/- 0.31)x10^-3, where the error is the combined experimental and theoretical uncertainty.
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We report on recent measurements of the branching fractions (BFs) for the decay channels B^0 -> {pi}^-l^+{ u}, B^+ -> {pi}^0l^+{ u}, B^+ -> {eta}l^+{ u}, B^+ -> {eta}l^+{ u}, B^0 -> {rho}^-l^+{ u} and B^+ -> {rho}^0l^+{ u}. We obtain very precise values of the total branching fractions for these decays, as well as partial branching fractions as a function of q^2 for the decay channels B^0 -> {pi}^-l^+{ u}, B^+ -> {eta}l^+{ u} and B^0 -> {rho}^-l^+{ u}. In particular, we use the partial branching fractions of the B^0 -> {pi}^-l^+{ u} decay channel and form-factor calculations to extract several values of |V_{ub}|. When we compared these values of |V_{ub}| to the one measured in inclusive semileptonic B decay, we find that two of them are consistent, within large theoretical uncertainties.
In this talk results of the study of the $D^0 to pi^- e^+ u$ decay channel, recorded by the BaBar detector at the c.m. energy close to 10.6 GeV, are reported. The branching fraction of this channel is measured relative to the $D^0 to K^- pi^+$ decay. The hadronic form factor, $f_{+,D}^{pi}(q^2)$, function of $q^2$, the four momentum transfer squared between the $D$ and the $pi$ mesons, is compared to various theoretical predictions, and the normalization $V_{cd} times f_{+,D}^{pi}(q^2=0)$ is extracted from a fit to data. Results are compared with Lattice QCD calculations. A new multipole model is applied which makes use of present information of resonant states contributing to the form factor. With the understanding of the $f_{+,D}^{pi}(q^2)$ form factor, and provided the relation between the $D^0 to pi^- e^+ u$ and $B^0 to pi^- e^+ u$ decay widths at the same pion energy, the CKM matrix element $V_{ub}$ is determined and compared to recent measurements. This method of extracting $V_{ub}$ will become competitive with new Lattice QCD calculations of the ratio of form factors.
We compute the $Btopiell u$ semileptonic form factors and update the determination of the CKM matrix element $|V_{ub}|$. We use the MILC asqtad ensembles with $N_f=2+1$ sea quarks at four different lattice spacings in the range $a approx 0.045$~fm to $0.12$~fm. The lattice form factors are extrapolated to the continuum limit using SU(2) staggered chiral perturbation theory in the hard pion limit, followed by an extrapolation in $q^2$ to the full kinematic range using a functional $z$-parameterization. The extrapolation is combined with the experimental measurements of the partial branching fraction to extract $|V_{ub}|$. Our preliminary result is $|V_{ub}|=(3.72pm 0.14)times 10^{-3}$, where the error reflects both the lattice and experimental uncertainties, which are now on par with each other.
We present a lattice quantum chromodynamics determination of the ratio of the scalar and vector form factors for two semileptonic decays of the $B_s$ meson: $B_s rightarrow K ell u$ and $B_s rightarrow D_s ell u$. In conjunction with future experimental data, our results for these correlated form factors will provide a new method to extract $|V_{ub}/V_{cb}|$, which may elucidate the current tension between exclusive and inclusive determinations of these Cabibbo-Kobayashi-Maskawa mixing matrix parameters. In addition to the form factor results, we determine the ratio of the differential decay rates, and forward-backward and polarization asymmetries, for the two decays.
We present a measurement of the charmless semileptonic decay $B^0topi^-ell^+ u$ using a data sample containing 657$times 10^6$ $Bbar{B}$ events collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider operating near the $Upsilon(4S)$ resonance. We determine the total branching fraction of the decay, $mathcal{B}(B^0topi^-ell^+ u)=(1.49pm 0.04{(mathrm{stat})}pm 0.07{(mathrm{syst})})times 10^{-4}$. We also report a new precise measurement of the differential decay rate, and extract the Cabibbo-Kobayashi-Maskawa matrix element $|V_{ub}|$ using model-independent and -dependent approaches. From a simultaneous fit to the measured differential decay rate and lattice QCD results, we obtain $|V_{ub}|=(3.43pm 0.33)times 10^{-3}$, where the error includes both statistical and systematic uncertainties.
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