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Register a new userThe $Bto pi ell u_ell$ semileptonic decay within the LCSR approach under heavy quark effective field theory
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The heavy quark effective field theory (HQEFT) provides an effective way to deal with the heavy meson decays. In the paper, we adopt two different correlators to derive the light-cone sum rules of the $B to pi$ transition form factors (TFFs) within the framework of HQEFT. We label those two LCSR results as LCSR-${cal U}$ and LCSR-${cal R}$, which are for conventional correlator and right-handed correlator, respectively. We observe that the correlation parameter $|rho_{rm RU}|$ for the branching ratio ${cal B}(B to pi l u_{l})$ is $sim 0.85$, implying the consistency of the LCSRs under different correlators. Moreover, we obtain $|V_{rm ub}|_{{rm LCSR}-{cal U}}=(3.45^{+0.28}_{-0.20}pm{0.13}_{rm{exp}})times10^{-3}$ and $|V_{rm ub}|_{{rm LCSR}-{cal R}} =(3.38^{+0.22}_{-0.16} pm{0.12}_{rm{exp}})times10^{-3}$. We then obtain $mathcal{R}_{pi}|_{{rm LCSR}-{cal U}}=0.68^{+0.10}_{-0.09}$ and $mathcal{R}_{pi}|_{{rm LCSR}-{cal R}}=0.65^{+0.13}_{-0.11}$, both of them agree with the Lattice QCD predictions. Thus the HQEFT provides a useful framework for studying the $B$ meson decays. Moreover, by using right-handed correlator, the twist-2 terms shall dominant the TFF $f^+(q^2)$, which approaches over $sim97%$ contribution in the whole $q^2$-region; and the large twist-3 uncertainty for the conventional correlator is greatly suppressed. One can thus adopt the LCSR-${cal R}$ prediction to test the properties of the various models for the pion twist-2 distribution amplitudes.
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After improving the knowledge about residua of the semileptonic form factor at its first two poles we show that $f_+^{Dpi}(q^2)$ is not saturated when compared with the experimental data. To fill the difference we approximate the rest of discontinuity by an effective pole and show that the data can be described very well with the position of the effective pole larger than the next excitation in the spectrum of $D^ast$ state. The results of fits with experimental data also suggest the validity of superconvergence which in the pole models translates to a vanishing of the sum of residua of the form factor at all poles. A similar discussion in the case of $Bto pi ell u_ell$ leads to the possibility of extracting $vert V_{ub}vert$, the error of which appears to be dominated by $g_{B^ast Bpi}$, which can be nowadays computed on the lattice. In evaluating the residua of the form factors at their nearest pole we needed the vector meson decay constants $f_{D^ast}$ and $f_{B^ast}$, which we computed by using the numerical simulations of QCD on the lattice with $N_{rm f}=2$ dynamical quarks. We obtain, $f_{D^ast}/f_D=1.208(27)$ and $f_{B^ast}/f_B=1.051(17)$.
The scaling behavior of semileptonic form-factors in Heavy to Light transitions is studied in the Heavy Quark Effective Theory. In the case of $Hrightarrow pi e u$ it is shown that the same scaling violations affecting the heavy meson decay constant will be present in the semileptonic form-factors.
We reconsider the QCD predictions for the radiative decay $Bto gamma ell u_ell$ with an energetic photon in the final state by taking into account the $1/E_gamma, 1/m_b$ power-suppressed hard-collinear and soft corrections from higher-twist $B$-meson light-cone distribution amplitudes (LCDAs). The soft contribution is estimated through a dispersion relation and light-cone QCD sum rules. The analysis of theoretical uncertainties and the dependence of the decay form factors on the leading-twist LCDA $phi_+(omega)$ shows that the latter dominates. The radiative leptonic decay is therefore well suited to constrain the parameters of $phi_+(omega)$, including the first inverse moment, $1/lambda_B$, from the expected high-statistics data of the BELLE II experiment.
In this paper, we make a detailed study about the $Dto V$ helicity form factors (HFFs) within the framework of QCD light-cone sum rule (LCSR) up to twist-4 accuracy. After extrapolating the LCSR predictions of HFFs to the whole physical $q^2$-region, we get the longitudinal, transverse and total $|V_{cq}|$-independent decay widths of semileptonic decay $Dto Vell^+ u_ell$. Meanwhile, the branching fractions of these decays are also obtained by using the $D^0(D^+)$-meson lifetime, which agree well with the BES-III results within errors. As a further step, we also investigate the differential and mean predictions for charged lepton (vector meson) polarization in the final state $P_{rm L,T}^ell$ ($F_{rm L,T}^ell$), the forward-backward asymmetry ${cal A}_{rm FB}^ell$, and the lepton-side convexity parameters ${cal C}_{rm F}^ell$. Our predictions are consistent with Covariant Confining Quark Model results within the errors. Thus, we think the LCSR approach for HFFs is applicable for dealing with the $D$-meson semileptonic decays.
We present a general study on exclusive semileptonic decays of heavy (B, D, B_s) to light (pi, rho, K, K^*) mesons in the framework of effective field theory of heavy quark. Transition matrix elements of these decays can be systematically characterized by a set of wave functions which are independent of the heavy quark mass except for the implicit scale dependence. Form factors for all these decays are calculated consistently within the effective theory framework using the light cone sum rule method at the leading order of 1/m_Q expansion. The branching ratios of these decays are evaluated, and the heavy and light flavor symmetry breaking effects are investigated. We also give comparison of our results and the predictions from other approaches, among which are the relations proposed recently in the framework of large energy effective theory.
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