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Register a new userA More Precise Extraction of |V_{cb}| in HQEFT of QCD
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The more precise extraction for the CKM matrix element |V_{cb}| in the heavy quark effective field theory (HQEFT) of QCD is studied from both exclusive and inclusive semileptonic B decays. The values of relevant nonperturbative parameters up to order 1/m^2_Q are estimated consistently in HQEFT of QCD. Using the most recent experimental data for B decay rates, |V_{cb}| is updated to be |V_{cb}| = 0.0395 pm 0.0011_{exp} pm 0.0019_{th} from Bto D^{ast} l u decay and |V_{cb}| = 0.0434 pm 0.0041_{exp} pm 0.0020_{th} from Bto D l u decay as well as |V_{cb}| = 0.0394 pm 0.0010_{exp} pm 0.0014_{th} from inclusive Bto X_c l u decay.
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The Cabibbo-Kobayashi-Maskawa parameter $|V_{cb}|$ plays an important role among the experimental constraints of the Yukawa sector of the Standard Model. The present status of our knowledge will be summarized with particular emphasis to the interplay between theoretical and experimental advances needed to improve upon present uncertainties.
The Cabibbo-Kobayashi-Maskawa (CKM) matrix element $vert V_{cb}vert$ is extracted from exclusive semileptonic $B to D^{(*)}$ decays adopting a novel unitarity-based approach which allows to determine in a full non-perturbative way the relevant hadronic form factors (FFs) in the whole kinematical range. By using existing lattice computations of the $B to D^{(*)}$ FFs at small recoil, we show that it is possible to extrapolate their behavior also at large recoil without assuming any specific momentum dependence. Thus, we address the extraction of $vert V_{cb}vert$ from the experimental data on the semileptonic $B to D^{(*)} ell u_ell$, obtaining $vert V_{cb}vert = (40.7 pm 1.2 ) cdot 10^{-3}$ from $B to D$ and $vert V_{cb}vert = (40.6 pm 1.6 ) cdot 10^{-3}$ from $B to D^*$. Our results, though still based on preliminary lattice data for the $B to D^*$ form factors, are consistent within $sim 1$ standard deviation with the most recent inclusive determination $vert V_{cb} vert_{incl} = (42.00 pm 0.65) cdot 10^{-3}$. We investigate also the issue of Lepton Flavor Universality thanks to new theoretical estimates of the ratios $R(D^{(*)})$, namely $R(D) = 0.289(8)$ and $R(D^{*}) = 0.249(21)$. Our findings differ respectively by $sim 1.6sigma$ and $sim1.8sigma$ from the latest experimental determinations.
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.
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 extract $|V_{cb}|$ from the available data in the decay $B to D^{(*)}ell u_{ell}$. Our analysis uses the $q^2(w)$ binned differential decay rates in different subsamples of $Bto Dell u_ell$ ($ell = e, mu$), while for the decay $Bto D^*ell u_ell$, the unfolded binned differential decay rates of four kinematic variables including the $q^2$ bins have been used. In the CLN and BGL parameterizations of the form factors, the combined fit to all the available data along with their correlations yields $|V_{cb}| = (39.77 pm 0.89)times 10^{-3}$ and $(40.90 pm 0.94)times 10^{-3}$ respectively. In these fits, we have used the inputs from lattice and light cone sum rule (LCSR) along with the data. Using our fit results and the HQET relations (with the known corrections included) amongst the form factors, and parameterizing the unknown higher order corrections (in the ratios of HQET form factors) with a conservative estimate of the normalizing parameters, we obtain $R(D^{*}) = 0.259 pm 0.006$ (CLN) and $R(D^*) = 0.257 pm 0.005$ (BGL).
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