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Register a new userThe $B to rho $ helicity form factors within the QCD light-cone sum rules
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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.
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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.
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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 present a new calculation of the semileptonic tree-level and flavor-changing neutral current form factors describing $B$-meson transitions to tensor mesons $T=D_2^*,K_2^*,a_2,f_2$ ($J^{P}=2^{+}$). We employ the QCD Light-Cone Sum Rules approach with $B$-meson distribution amplitudes. We go beyond the leading-twist accuracy and provide analytically, for the first time, higher-twist corrections for the two-particle contributions up to twist four terms. We observe that the impact of higher twist terms to the sum rules is noticeable. We study the phenomenological implications of our results on the radiative ${B} to K_2^{*}gamma$ and semileptonic ${B} to D_2^* ell {bar u}_ell$, ${B} to K_2^{*}ell^+ell^-$ decays.
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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