Measurement of R(D)\mathcal{R}(D) and R(D∗)\mathcal{R}(D^{\ast}) with a semileptonic tagging method

We report a measurement of the ratios of branching fractions $\mathcal{R}(D) = {\cal B}(\bar{B} \to D \tau^- \bar{\nu}_{\tau})/{\cal B}(\bar{B} \to D \ell^- \bar{\nu}_{\ell})$ and $\mathcal{R}(D^{\ast}) = {\cal B}(\bar{B} \to D^* \tau^- \bar{\nu}_{\tau})/{\cal B}(\bar{B} \to D^* \ell^- \bar{\nu}_{\ell})$, where $\ell$ denotes an electron or a muon. The results are based on a data sample containing $772\times10^6$ $B\bar{B}$ events recorded at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. The analysis utilizes a method where the tag-side $B$ meson is reconstructed in a semileptonic decay mode, and the signal-side $\tau$ is reconstructed in a purely leptonic decay. The measured values are $\mathcal{R}(D)= 0.307 \pm 0.037 \pm 0.016$ and $\mathcal{R}(D^{\ast})= 0.283 \pm 0.018 \pm 0.014$, where the first uncertainties are statistical and the second are systematic. These results are in agreement with the Standard Model predictions within $0.2$ and $1.1$ standard deviations, respectively, while their combination agrees with the Standard Model predictions within $1.2$ standard deviations

Test of lepton flavor universality in B→K∗ℓ+ℓ−{B\to K^\ast\ell^+\ell^-} decays at Belle

We present a measurement of $R_{K^{\ast}}$, the ratio of the branching fractions ${\cal B}(B\to K^\ast \mu^+ \mu^-)$ and ${\cal B}(B\to K^\ast e^+ e^-)$, for both charged and neutral $B$ mesons. The ratio for charged $B$ mesons, $R_{K{^{\ast +}}}$, is the first measurement ever performed. The analysis is based on a data sample of $711~\mathrm{fb}^{-1}$, containing $772\times 10^{6}$ $B\bar B$ events, recorded at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider

Test of lepton flavor universality and search for lepton flavor violation in B→KℓℓB \rightarrow K\ell \ell decays

International audienceWe present measurements of the branching fractions for the decays B → Kμ$^{+}$μ$^{−}$ and B → Ke$^{+}$e$^{−}$, and their ratio (R$_{K}$), using a data sample of 711 fb$^{−1}$ that contains 772 × 10$^{6} B\overline{B}$ events. The data were collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e$^{+}$e$^{−}$ collider. The ratio R$_{K}$ is measured in five bins of dilepton invariant-mass-squared (q$^{2}$): q$^{2}$ ∈ (0.1, 4.0), (4.00, 8.12), (1.0, 6.0), (10.2, 12.8) and (> 14.18) GeV$^{2}$/c$^{4}$, along with the whole q$^{2}$ region. The R$_{K}$ value for q$^{2}$ ∈ (1.0, 6.0) GeV$^{2}$/c$^{4}$ is ${1.03}_{-0.24}^{+0.28}$ ± 0.01. The first and second uncertainties listed are statistical and systematic, respectively. All results for R$_{K}$ are consistent with Standard Model predictions. We also measure CP-averaged isospin asymmetries in the same q$^{2}$ bins. The results are consistent with a null asymmetry, with the largest difference of 2.6 standard deviations occurring for the q$^{2}$ ∈ (1.0, 6.0) GeV$^{2}$/c$^{4}$ bin in the mode with muon final states. The measured differential branching fractions, $d\mathrm{\mathcal{B}}$/dq$^{2}$, are consistent with theoretical predictions for charged B decays, while the corresponding values are below the expectations for neutral B decays. We have also searched for lepton-flavor-violating B → Kμ$^{±}$e$^{∓}$ decays and set 90% confidence-level upper limits on the branching fraction in the range of 10$^{−8}$ for B$^{+}$ → K$^{+}$μ$^{±}$e$^{∓}$, and B$^{0}$ → K$^{0}$μ$^{±}$e$^{∓}$ modes.[graphic not available: see fulltext

Measurement of the D∗−D^{\ast-} polarization in the decay B0→D∗−τ+ντB^0 \to D^{\ast -}\tau^+\nu_{\tau}

International audienceWe report the first measurement of the $D^{\ast -}$ meson polarization in the decay $B^0 \to D^{*-} \tau^+\nu_{\tau}$ using the full data sample of 772$\times 10^6$ $B\bar{B}$ pairs recorded with the Belle detector at the KEKB electron-positron collider. Our result, $F_L^{D^\ast} = 0.60 \pm 0.08 ({\rm stat}) \pm 0.04 ({\rm sys})$, where $F_L^{D^\ast}$ denotes the $D^{\ast-}$ meson longitudinal polarization fraction, agrees within about $1.7$ standard deviations of the standard model prediction

Study of χbJ(nP)→ωΥ(1S)\chi_{bJ}(nP) \rightarrow \omega \Upsilon(1S) at Belle

We report results from a study of hadronic transitions of the $\chi_{bJ}(nP)$ states of bottomonium at Belle. The $P$-wave states are reconstructed in transitions to the $\Upsilon(1S)$ with the emission of an $\omega$ meson. The transitions of the $n=2$ triplet states provide a unique laboratory in which to study nonrelativistic quantum chromodynamics, as the kinematic threshold for production of an $\omega$ and $\Upsilon(1S)$ lies between the $J=0$ and $J=1$ states. A search for the $\chi_{bJ}(3P)$ states is also reported

Rediscovery of B0→J/ψKL0B^0 \rightarrow J/\psi K^0_L at Belle II

We present preliminary results on the reconstruction of the $B^0\to J\mskip 1mu / \psi\mskip 2mu K^0_{\scriptscriptstyle L}$ decay, where $J\mskip 1mu / \psi\mskip 2mu\to\mu^+\mu^-$ or $e^+e^-$. Using a dataset corresponding to a luminosity of 62.8\pm0.6\mbox{fb}^{-1} collected by the Belle II experiment at the SuperKEKB asymmetric energy $e^+e^-$ collider, we measure a total of $267\pm21$ candidates with $J\mskip 1mu / \psi\mskip 2mu\to\mu^+\mu^-$ and $226\pm20$ with with $J\mskip 1mu / \psi\mskip 2mu\to e^+e^-$. The quoted errors are statistical only

Measurement of the BB−^{-} →\rightarrow DD0^{0}ℓ\ell−^{-}νˉ\bar{\nu}ℓ_{\ell} Branching Fraction in 62.8 fb−1^{-1} of Belle II data

We report a measurement of the branching fraction of the semileptonic decay $B$$^{-}$ $\rightarrow$ $D$$^{0}$$\ell$$^{-}$$\bar{\nu}$$_{\ell}$ (and its charge conjugate) using 62.8 fb$^{-1}$ of $\Upsilon$(4$S$) $\rightarrow$ $B$$\bar{B}$ data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy $e$$^{+}$ $e$$^{-}$ collider. The neutral charm meson is searched for in the decay mode $D$$^{0}$ $\rightarrow$ $K$$^{-}$ $\pi$$^{+}$ and combined with a properly charged identified lepton (electron or muon) to reconstruct this decay. No reconstruction of the second $B$ meson in the $\Upsilon$(4$S$) event is performed. We obtain $B$($D$$^{0}$$\ell$$^{-}$$\bar{\nu}$$_{\ell}$) = (2.29 $\pm$ 0.05 $_{stat}$ $\pm$ 0.08$_{syst}$, in agreement with the world average of this decay. We also determine the ratio of the electron to muon branching fractions to be $R$($e$/$\mu$) = 1.04 $\pm$ 0.05$_{stat}$ $\pm$ 0.03$_{syst}$ and observe no deviation from lepton universality