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Register a new userV_{ub}, V_{cb} and Decay Constants in Effective Field Theory of Heavy Quarks
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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.
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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.
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.
B --> rho l nu decay is analyzed in the effective theory of heavy quark with infinite mass limit. The matrix element relevant to the heavy to light vector meson semileptonic decays is parametrized by a set of four heavy flavor-spin independent universal wave functions at the leading order of effective theory. The form factors are calculated at the leading 1/m_Q order using the light cone sum rule method in the framework of effective theory. |V_{ub}| is then extracted via B --> rho l nu decay mode.
We discuss the impact of the recent $mathcal{O}(alpha_s^3)$ calculations of the semileptonic width of the $b$ quark and of the relation between pole and kinetic heavy quark masses by Fael et al. on the inclusive determination of $|V_{cb}|$. The most notable effects are a small increase in the value $|V_{cb}|$ and a reduction of the uncertainty. Our final result is $|V_{cb}|=42.16(50), 10^{-3}$.
We discuss the impact of the recent untagged analysis of ${B}^0rightarrow D^{*}lbar{ u}_l$ decays by the Belle Collaboration on the extraction of the CKM element $|V_{cb}|$ and provide updated SM predictions for the $bto ctau u$ observables $R(D^*)$, $P_tau$, and $F_L^{D^*}$. The value of $|V_{cb}|$ that we find is about $2sigma$ from the one from inclusive semileptonic $B$ decays, and is very sensitive to the slope of the form factor at zero recoil which should soon become available from lattice calculations.
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