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Register a new userFirst observation of the decay $B_s^0 to K^-mu^+ u_mu$ and a measurement of $|V_{ub}|/|V_{cb}|$
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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.
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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.
A new framework of heavy quark effective field theory (HQEFT) is studied and compared with the usual heavy quark effective theory (HQET). $|V_{ub}|$, $|V_{cb}|$ and heavy meson decay constants are extracted in the new framework. HQEFT can yield reasonable results for both exclusive and inclusive decays.
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 perform the simultaneous $|V_{ub}|$ and $|V_{cb}|$ extractions with only the exclusive $Lambda_b$ decays of $Lambda_bto (p,Lambda_c^+)mubar u_mu$, $Lambda_bto ppi^-$ and $Lambda_bto Lambda_c^+ (pi^-, D^-)$. We obtain that $|V_{ub}|=(3.7pm 0.3)times 10^{-3}$ and $|V_{cb}|=(45.9pm 2.7)times 10^{-3}$. Our value of $|V_{ub}|$ is larger than that of $(3.27pm 0.15pm 0.16pm 0.06)times 10^{-3}$, previously extracted by the LHC Collaboration from the exclusive $Lambda_b$ decays also, but nearly identical to $(3.72pm 0.19)times 10^{-3}$ from the exclusive $B$ decays. On the other hand, our extracted result of $|V_{cb}|$ favors the value of $(42.2pm 0.8)times 10^{-3}$ from the inclusive $B$ 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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