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Register a new user$D to P(pi,K)$ helicity form factors within light-cone sum rule approach
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In this paper, the $Dto P(pi, K)$ helicity form factors (HFFs) are studied by applying the QCD light-cone sum rule (LCSR) approach. The calculation accuracy is up to next-to-leading order (NLO) gluon radiation correction of twist-(2,3) distribution amplitude. The resultant HFFs at large recoil point are ${cal P}_{t,0}^pi(0) = 0.688^{+0.020}_{-0.024}$, ${cal P}_{t,0}^K(0)=0.780^{+0.024}_{-0.029}$. In which, the contributions from three particles of the leading order (LO) are so small that can be safely neglected, and the maximal contribution of the NLO gluon radiation correction for ${cal P}_{t,0}^{pi,K}(0)$ is less than $3%$. After extrapolating the LCSR predictions for these HFFs to whole $q^2$-region, we obtain the decay widths for semileptonic decay processes $Dto Pell u_ell$, which are consistent with BES-III collaboration predictions within errors. After considering the $D^{+}/D^{0}$-meson lifetime, we give the branching fractions of $Dto Pell u_ell$ with $ell = e, mu$, our predictions also agree with BES-III collaboration within errors, especially for $Dto pi ell u_ell$ decay process. Finally, we present the forward-backward asymmetry ${cal A}_{rm FB}^ell(q^2)$ and lepton convexity parameter ${cal C}_F^ell(q^2)$, and further calculate the mean value of these two observations $langle{cal A}_{rm FB}^ellrangle$ and $langle{cal C}_F^ellrangle$, which may provide a way to test those HFFs in future experiments.
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We study the $B to rho$ helicity form factors (HFFs) by applying the light-cone sum rules up to twist-4 accuracy. The HFF has some advantages in comparison to the conventionally calculated transition form factors, such as the HFF parameterization can be achieved via diagonalizable unitarity relations and etc. At the large recoil point, only the $rho$-meson longitudinal component contributes to the HFFs, and we have $mathcal{H}_{rho,0}(0)=0.435^{+0.055}_{-0.045}$ and $mathcal{H}_{rho,{1,2}}(0)equiv 0$. We extrapolate the HFFs to physically allowable $q^2$-region and apply them to the $B to rho$ semileptonic decay. We observe that the $rho$-meson longitudinal component dominates its differential decay width in low $q^2$-region, and its transverse component dominates the high $q^2$-region. Two ratios $R_{rm low}$ and $R_{rm high}$ are used to characterize those properties, and our LCSR calculation gives, $R_{rm low}=0.967^{+0.305}_{-0.284}$ and $R_{rm high}=0.219^{+0.058}_{-0.070}$, which agree with the BaBar measurements within errors.
We present an improved QCD light-cone sum rule (LCSR) calculation of the B -> K and Bs -> K form factors, by including SU(3)-symmetry breaking corrections. We use recently updated K-meson distribution amplitudes which incorporate the complete SU(3)-breaking structure. By applying the method of the direct integration in the complex plane, which is presented in a detail, the analytical extraction of the imaginary parts of LCSR hard-scattering amplitudes becomes unnecessary and therefore the complexity of the calculation is greatly reduced. The values obtained for the relevant B_{(s)} -> K form factors are as follows: f^+_{BK}(0)= 0.36^{+0.05}_{-0.04}, f^+_{B_sK}(0)= 0.30^{+0.04}_{-0.03} and f^T_{BK}(0)= 0.38pm 0.05, f^T_{B_sK}(0)= 0.30pm 0.05. By comparing with the B -> pi form factors extracted recently by the same method, we find the following SU(3) violation among the B -> light form factors: f^+_{BK}(0)/f^+_{Bpi}(0) = 1.38^{+0.11}_{-0.10}, f^+_{B_sK}(0)/f^+_{Bpi}(0) = 1.15^{+0.17}_{-0.09}, f^T_{BK}(0)/f^T_{Bpi}(0) = 1.49^{+0.18}_{-0.06} and f^T_{B_sK}(0)/f^T_{Bpi}(0) = 1.17^{+0.15}_{-0.11}.
We reconsider and update the QCD light-cone sum rules for $Bto pi$ form factors. The gluon radiative corrections to the twist-2 and twist-3 terms in the correlation functions are calculated. The $bar{MS}$ $b$-quark mass is employed, instead of the one-loop pole mass used in the previous analyses. The light-cone sum rule for $f^+_{Bpi}(q^2)$ is fitted to the measured $q^2$-distribution in $Bto pi l u_l$, fixing the input parameters with the largest uncertainty: the Gegenbauer moments of the pion distribution amplitude. For the $Bto pi$ vector form factor at zero momentum transfer we predict $f^+_{Bpi}(0)= 0.26^{+0.04}_{-0.03}$. Combining it with the value of the product $|V_{ub}f^+_{Bpi}(0)|$ extracted from experiment, we obtain $|V_{ub}|=(3.5pm 0.4pm 0.2pm 0.1) times 10^{-3}$. In addition, the scalar and penguin $Bto pi$ form factors $f^0_{Bpi}(q^2)$ and $f^T_{Bpi}(q^2)$ are calculated.
We derive new QCD sum rules for $Bto D$ and $Bto D^*$ form factors. The underlying correlation functions are expanded near the light-cone in terms of $B$-meson distribution amplitudes defined in HQET, whereas the $c$-quark mass is kept finite. The leading-order contributions of two- and three-particle distribution amplitudes are taken into account. From the resulting light-cone sum rules we calculate all $Bto Dst $ form factors in the region of small momentum transfer (maximal recoil). In the infinite heavy-quark mass limit the sum rules reduce to a single expression for the Isgur-Wise function. We compare our predictions with the form factors extracted from experimental $Bto Dst l u_l$ decay rates fitted to dispersive parameterizations.
We compute perturbative corrections to $B to pi$ form factors from QCD light-cone sum rules with $B$-meson distribution amplitudes. Applying the method of regions we demonstrate factorization of the vacuum-to-$B$-meson correlation function defined with an interpolating current for pion, at one-loop level, explicitly in the heavy quark limit. The short-distance functions in the factorization formulae of the correlation function involves both hard and hard-collinear scales; and these functions can be further factorized into hard coefficients by integrating out the hard fluctuations and jet functions encoding the hard-collinear information. Resummation of large logarithms in the short-distance functions is then achieved via the standard renormalization-group approach. We further show that structures of the factorization formulae for $f_{B pi}^{+}(q^2)$ and $f_{B pi}^{0}(q^2)$ at large hadronic recoil from QCD light-cone sum rules match that derived in QCD factorization. In particular, we perform an exploratory phenomenological analysis of $B to pi$ form factors, paying attention to various sources of perturbative and systematic uncertainties, and extract $|V_{ub}|= left(3.05^{+0.54}_{-0.38} |_{rm th.} pm 0.09 |_{rm exp.}right) times 10^{-3}$ with the inverse moment of the $B$-meson distribution amplitude $phi_B^{+}(omega)$ determined by reproducing $f_{B pi}^{+}(q^2=0)$ obtained from the light-cone sum rules with $pi$ distribution amplitudes. Furthermore, we present the invariant-mass distributions of the lepton pair for $B to pi ell u_{ell}$ ($ell= mu ,, tau$) in the whole kinematic region. Finally, we discuss non-valence Fock state contributions to the $B to pi$ form factors $f_{B pi}^{+}(q^2)$ and $f_{B pi}^{0}(q^2)$ in brief.
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