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[en] As part of the BaBar project at SLAC to study the properties of B mesons, we have carried out a study of the exclusive charmless semileptonic decay mode B → wlv, which can be used to determine the Cabbibo-Kobayashi-Maskawa matrix element V_ub. Using simulated event samples, this study focuses on determining criteria on variables for selection of B → wlv signal and suppression of background from other types of B(bar B) events and continuum processes. In addition, we determine optimal cuts on variables to ensure a good neutrino reconstruction. With these selection cuts, we were able to achieve a signal-to-background ratio of 0.68 and a signal efficiency of the order of 1%. Applying these cuts to a sample of 83 million B(bar B) events recorded by BaBar in e⁺e^- collisions at the Υ(4S) resonance, we obtain a yield of 115 ± 19 B → wlv decays

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[en] Here, we repormore » t a measurement of the inclusive semileptonic B s 0 branching fraction in a 121 fb - 1 data sample collected near the Υ (5 S) resonance with the Belle detector at the KEKB asymmetric energy e + e - collider. Events with B s 0 (*) B ¯ s 0 (*) pairs are selected by reconstructing a tag side D s + and identifying a signal side lepton ℓ + (ℓ = e , μ) that is required to have the same-sign charge to ensure that both originate from different B s 0 mesons. The B s 0 → X - ℓ + ν ℓ branching fraction is extracted from the ratio of the measured yields of D s + mesons and D s + ℓ + pairs and the known production and branching fractions. The inclusive semileptonic branching fraction is measured to be [ 10.6 ± 0.5 (stat) ± 0.7 (syst) ] % .

[en] We report the measurement of the direct CP asymmetry in the radiative B¯→ X_s+dγ decay using a data sample of (772 ± 11) × 10⁶ BB¯ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^– collider. Here, the CP asymmetry is measured as a function of the photon energy threshold. For E${}_{\text{γ<!-- ?? -->}}^{\ast <!--\; ???\; -->}$ ≥ 2.1 GeV, where E${}_{\text{γ<!-- ?? -->}}^{\ast <!--\; ???\; -->}$ is the photon energy in the center-of-mass frame, we obtain A_CP(B¯ → X_s+dγ) = (2.2 ± 3.9 ± 0.9)%, consistent with the standard model prediction.

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[en] Here, we report a measurement of the inclusive semileptonic $B_s^0$ branching fraction in a $121{\mathrm{fb}}^{-1}$ data sample collected near the ${\rm Y}(5S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^{+}{e}^{-}$ collider. Events with $B_s^{0(*)}{\overline{B}}_s^{0(*)}$ 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 $B_s^0\to X^{-}{\ell }^{+}{\nu }_{\ell }$ 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 $[10.6\pm 0.5(\mathrm{stat})\pm 0.7(\mathrm{syst})]\%$.

[en] We report branching fraction measurements of the decays B⁺ → ηℓ⁺νℓ and B⁺ → η'ℓ⁺νℓ based on 711 fb^–1 of data collected near the Υ(4S) resonance with the Belle experiment at the KEKB asymmetric-energy e⁺e^– collider. This data sample contains 772 million BB¯ events. One of the two B mesons is fully reconstructed in a hadronic decay mode. Among the remaining (“signal-B”) daughters, we search for the η meson in two decay channels, η → γγ and η → π⁺π^–π⁰, and reconstruct the η' meson in η' → ηπ⁺π^– with subsequent decay of the η into γγ. Combining the two η modes and using an extended maximum likelihood, the B⁺ → ηℓ⁺νℓ branching fraction is measured to be (4.2 ± 1.1(stat.) ± 0.3(syst.)) × 10^–5. For B⁺ → η'ℓ⁺νℓ, we observe no significant signal and set an upper limit of 0.72 × 10^–4 at 90% confidence level.