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Register a new userMeasurement of the branching fraction of B^+ -> tau^+ nu_tau decays with the semileptonic tagging method
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We report a measurement of the branching fraction of B^+ -> tau^+ nu_tau decays using a data sample of 772 x 10^6 BBbar pairs, collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We reconstruct the accompanying B meson in a semileptonic decay and detect the recoiling B candidate in the decay channel B^+ -> tau^+ nu_tau. We obtain a branching fraction of BR(B^+ -> tau^+ nu_tau) = [1.25 +- 0.28 (stat.) +- 0.27 (syst.)] x 10^-4. This result is in good agreement with previous measurements and the expectation from the calculation based on the Standard Model.
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We report a measurement of the branching fraction of $B^+ to tau^+ u_tau$ decays using a data sample of $772 times 10^6 B bar{B}$ pairs, collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We reconstruct the accompanying $B$ meson in a semileptonic decay and detect the $B^+ to tau^+ u_tau$ candidate in the recoiling event. We obtain a branching fraction of ${cal B}(B^+ to tau^+ u_tau) = [1.25 pm 0.28 ({rm stat.}) pm 0.27({rm syst.})] times 10^{-4}$. This result is in good agreement with previous measurements and the expectation from calculations based on the Standard Model.
Using a sample of tagged D_s decays collected near the D^*_s D_s peak production energy in e+e- collisions with the CLEO-c detector, we study the leptonic decay D^+_s to tau^+ nu_tau via the decay channel tau^+ to e^+ nu_e bar{nu}_tau. We measure B(D^+_s to tau^+ nu_tau) = (6.17 +- 0.71 +- 0.34) %, where the first error is statistical and the second systematic. Combining this result with our measurements of D^+_s to mu^+ nu_mu and D^+_s to tau^+ nu_tau (via tau^+ to pi^+ bar{nu}_tau), we determine f_{D_s} = (274 +- 10 +- 5) MeV.
We report a measurement of ratio ${cal R}(D^*) = {cal B}(bar{B}^0 rightarrow D^{*+} tau^- bar{ u}_{tau})/{cal B}(bar{B}^0 rightarrow D^{*+} ell^- bar{ u}_{ell})$, where $ell$ denotes an electron or a muon. The results are based on a data sample containing $772times10^6$ $Bbar{B}$ pairs recorded at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. We select a sample of $B^0 bar{B}^0$ pairs by reconstructing both $B$ mesons in semileptonic decays to $D^{*mp} ell^{pm}$. We measure ${cal R}(D^*)= 0.302 pm 0.030({rm stat)} pm 0.011({rm syst)}$, which is within $1.6 sigma$ of the Standard Model theoretical expectation, where $sigma$ is the standard deviation including systematic uncertainties.
We report a measurement of the ratio ${cal R}(D^*) = {cal B}(bar{B}^0 rightarrow D^{*+} tau^- bar{ u}_{tau})/{cal B}(bar{B}^0 rightarrow D^{*+} ell^- bar{ u}_{ell})$, where $ell$ denotes an electron or a muon. The results are based on a data sample containing $772times10^6$ $Bbar{B}$ pairs recorded at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. We select a sample of $B^0 bar{B}^0$ pairs by reconstructing both $B$ mesons in semileptonic decays to $D^{*mp} ell^{pm}$. We measure ${cal R}(D^*)= 0.302 pm 0.030({rm stat)} pm 0.011({rm syst)}$, which is within $1.6 sigma$ of the Standard Model theoretical expectation, where the standard deviation $sigma$ includes systematic uncertainties. We use this measurement to constrain several scenarios of new physics in a model-independent approach.
The ratio of branching fractions ${cal{R}}(D^{*-})equiv {cal{B}}(B^0 to D^{*-} tau^+ u_{tau})/{cal{B}}(B^0 to D^{*-} mu^+ u_{mu})$ is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3$~$fb$^{-1}$. The $tau$ lepton is reconstructed with three charged pions in the final state. A novel method is used that exploits the different vertex topologies of signal and backgrounds to isolate samples of semitauonic decays of $b$ hadrons with high purity. Using the $B^0 to D^{*-}pi^+pi^-pi^+$ decay as the normalization channel, the ratio ${cal{B}}(B^0 to D^{*-} tau^+ u_{tau})/{cal{B}}(B^0 to D^{*-}pi^+pi^-pi^+)$ is measured to be $1.97 pm 0.13 pm 0.18$, where the first uncertainty is statistical and the second systematic. An average of branching fraction measurements for the normalization channel is used to derive ${cal{B}}(B^0 to D^{*-} tau^+ u_{tau}) = (1.42 pm 0.094 pm 0.129 pm 0.054) %$, where the third uncertainty is due to the limited knowledge of ${cal{B}}(B^0to D^{*-}pi^+pi^-pi^+)$. A test of lepton flavor universality is performed using the well-measured branching fraction ${cal{B}}(B^0 to D^{*-} mu^+ u_{mu})$ to compute ${cal{R}}(D^{*-}) = 0.291 pm 0.019 pm 0.026 pm 0.013$, where the third uncertainty originates from the uncertainties on ${cal{B}}(B^0 to D^{*-}pi^+pi^-pi^+)$ and ${cal{B}}(B^0 to D^{*-} mu^+ u_{mu})$. This measurement is in agreement with the Standard Model prediction and with previous measurements.
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