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Register a new userMeasurement of $|V_{cb}|$ with $B_s^0 to D_s^{(*)-} mu^+ u_{mu}$ decays
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The element $|V_{cb}|$ of the Cabibbo-Kobayashi-Maskawa matrix is measured using semileptonic $B_s^0$ decays produced in proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. Rates of $B_s^0 to D_s^{-} mu^+ u_{mu}$ and $B_s^0 to D_s^{*-} mu^+ u_{mu}$ decays are analyzed using hadronic form-factor parametrizations derived either by Caprini, Lellouch and Neubert (CLN) or by Boyd, Grinstein and Lebed (BGL). The measured values of $|V_{cb}|$ are ${(41.4 pm 0.6 pm 0.9 pm 1.2)times 10^{-3}}$ and ${(42.3 pm 0.8 pm 0.9 pm 1.2)times 10^{-3}}$ in the CLN and BGL parametrization, respectively. The first uncertainty is statistical, the second systematic, and the third is due to the external inputs used in the measurement. These results are in agreement with those obtained from decays of $B^+$ and $B^0$ mesons. They are the first determinations of $|V_{cb}|$ at a hadron-collider experiment and the first using $B_s^0$ meson decays.
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The first observation of the suppressed semileptonic $B_s^0 to K^-mu^+ u_mu$ decay is reported. Using a data sample recorded in {it pp} collisions in 2012 with the LHCb detector, corresponding to an integrated luminosity of 2 $mathrm{fb}^{-1}$, the branching fraction mbox{$mathcal{B}(B_s^0 to K^-mu^+ u_mu)$} is measured to be $(1.06pm0.05~(mathrm{stat})pm0.08~(mathrm{syst}))times 10^{-4}$, where the first uncertainty is statistical and the second one represents the combined systematic uncertainties. The decay $B_s^0 to D_s^-mu^+ u_mu$, where $D_s^-$ is reconstructed in the final state $K^+K^-pi^-$, is used as a normalization channel to minimize the experimental systematic uncertainty. Theoretical calculations on the form factors of the $B_s^0 to K^-$ and $B_s^0 to D_s^-$ transitions are employed to determine the ratio of the CKM matrix elements ${|V_{ub}|}/{|V_{cb}|}$ at low and high $B_s^0 to K^-$ momentum transfer.
The shape of the $B_s^0rightarrow D_s^{*-}mu^+ u_{mu}$ differential decay rate is obtained as a function of the hadron recoil using proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 fb$^{-1}$ collected by the LHCb detector. The $B_s^0rightarrow D_s^{*-}mu^+ u_{mu}$ decay is reconstructed through the decays $D_s^{*-}rightarrow D_s^{-}gamma$ and $D_s^{-}rightarrow K^-K^+pi^-$. The differential decay rate is fitted with the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) parametrisations of the form factors, and the relevant quantities for both are extracted.
We observe a net beam-excess of $8.7 pm 6.3$ (stat) $pm 2.4$ (syst) events, above 160 MeV, resulting from the charged-current reaction of $ u_{mu}$ and/or $bar u_{mu}$ on C and H in the LSND detector. No beam related muon background is expected in this energy regime. Within an analysis framework of $pi^0 to u_{mu}bar u_{mu}$, we set a direct upper limit for this branching ratio of $Gamma(pi^0 to u_mu bar u_mu) / Gamma(pi^0 to all) < 1.6 times 10^{-6}$ at 90% confidence level.
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$^{-1}$. For the first time ${cal{R}}(D^{*-})$ is determined using the $tau$ lepton decays with three charged pions in the final state. The $B^0 to D^{*-} tau^+ u_{tau}$ yield is normalized to that of the $B^0to D^{*-} pi^+pi^-pi^+$ mode, providing a measurement of ${cal{B}}(B^0to D^{*-}tau^+ u_{tau})/{cal{B}}(B^0to D^{*-}pi^+pi^-pi^+) = 1.97 pm 0.13 pm 0.18$, where the first uncertainty is statistical and the second systematic. The value of ${cal{B}}(B^0 to D^{*-} tau^+ u_{tau}) = (1.42 pm 0.094 pm 0.129 pm 0.054)% $ is obtained, where the third uncertainty is due to the limited knowledge of the branching fraction of the normalization mode. Using the well-measured branching fraction of the $B^0 to D^{*-} mu^+ u_{mu}$ decay, a value of ${cal{R}}(D^{*-}) = 0.291 pm 0.019 pm 0.026 pm 0.013$ is established, where the third uncertainty is due to the limited knowledge of the branching fractions of the normalization and $B^0to D^{*-}mu^+ u_{mu}$ modes. This measurement is in agreement with the Standard Model prediction and with previous results.
By analyzing 482 pb$^{-1}$ of $e^+e^-$ collision data collected at the center-of-mass energy $sqrt s=4.009$ GeV with the BESIII detector, we measure the %absolute branching fractions for the semi-leptonic decays $D_{s}^{+}to phi e^{+} u_{e}$, $phi mu^{+} u_{mu}$, $eta mu^{+} u_{mu}$ and $etamu^{+} u_{mu}$ to be ${mathcal B}(D_{s}^{+}tophi e^{+} u_{e})=(2.26pm0.45pm0.09)$%, ${mathcal B}(D_{s}^{+}tophi mu^{+} u_{mu})=(1.94pm0.53pm0.09)$%, ${mathcal B}(D_{s}^{+}toeta mu^{+} u_{mu})=(2.42pm0.46pm0.11)$% and ${mathcal B}(D_{s}^{+}toetamu^{+} u_{mu}) = (1.06pm0.54pm0.07)$%, where the first and second uncertainties are statistical and systematic, respectively. The branching fractions for the three semi-muonic decays $D_s^+tophi mu^+ u_mu, eta mu^+ u_mu$ and $eta mu^+ u_mu$ are determined for the first time and that of $D^+_sto phi e^+ u_e$ is consistent with the world average value within uncertainties.
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