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Register a new userQCD corrections to $B to pi$ form factors from light-cone sum rules
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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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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 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 compute perturbative QCD corrections to $B to D$ form factors at leading power in $Lambda/m_b$, at large hadronic recoil, from the light-cone sum rules (LCSR) with $B$-meson distribution amplitudes in HQET. QCD factorization for the vacuum-to-$B$-meson correlation function with an interpolating current for the $D$-meson is demonstrated explicitly at one loop with the power counting scheme $m_c sim {cal O} left (sqrt{Lambda , m_b} right ) $. The jet functions encoding information of the hard-collinear dynamics in the above-mentioned correlation function are complicated by the appearance of an additional hard-collinear scale $m_c$, compared to the counterparts entering the factorization formula of the vacuum-to-$B$-meson correction function for the construction of $B to pi$ from factors. Inspecting the next-to-leading-logarithmic sum rules for the form factors of $B to D ell u$ indicates that perturbative corrections to the hard-collinear functions are more profound than that for the hard functions, with the default theory inputs, in the physical kinematic region. We further compute the subleading power correction induced by the three-particle quark-gluon distribution amplitudes of the $B$-meson at tree level employing the background gluon field approach. The LCSR predictions for the semileptonic $B to D ell u$ form factors are then extrapolated to the entire kinematic region with the $z$-series parametrization. Phenomenological implications of our determinations for the form factors $f_{BD}^{+, 0}(q^2)$ are explored by investigating the (differential) branching fractions and the $R(D)$ ratio of $B to D ell u$ and by determining the CKM matrix element $|V_{cb}|$ from the total decay rate of $B to D mu u_{mu}$.
We update QCD calculations of $B to pi, K$ form factors at large hadronic recoil by including the subleading-power corrections from the higher-twist $B$-meson light-cone distribution amplitudes (LCDAs) up to the twist-six accuracy and the strange-quark mass effects at leading-power in $Lambda/m_b$ from the twist-two $B$-meson LCDA $phi_B^{+}(omega, mu)$. The higher-twist corrections from both the two-particle and three-particle $B$-meson LCDAs are computed from the light-cone QCD sum rules (LCSR) at tree level. In particular, we construct the local duality model for the twist-five and -six $B$-meson LCDAs, in agreement with the corresponding asymptotic behaviours at small quark and gluon momenta, employing the QCD sum rules in heavy quark effective theory at leading order in $alpha_s$. The strange quark mass effects in semileptonic $B to K$ form factors yield the leading-power contribution in the heavy quark expansion, consistent with the power-counting analysis in soft-collinear effective theory, and they are also computed from the LCSR approach due to the appearance of the rapidity singularities. We further explore the phenomenological aspects of the semileptonic $B to pi ell u$ decays and the rare exclusive processes $B to K u u$, including the determination of the CKM matrix element $|V_{ub}|$, the normalized differential $q^2$ distributions and precision observables defined by the ratios of branching fractions for the above-mentioned two channels in the same intervals of $q^2$.
We calculate the $Dto P$ transition form factors within the framework of the light-cone QCD sum rules (LCSR) with the $D$-meson light-cone distribution amplitudes (LCDAs). The next-to-leading power (NLP) corrections to the vacuum-to-$D$-meson correlation function are considered, and the NLP corrections from the high-twist $D$-meson LCDAs and the SU(3) breaking effect from strange quark mass are investigated. Adopting the exponential model of the $D$-meson LCDAs,the predicted SU(3) flavor symmetry breaking effects are $R_{SU(3)}^{+,0}=1.12$ and $R_{SU(3)}^{T}=1.39$, respectively, which confirms the results from LCSR with pion LCDA. The numerical predictions of the form factors show that the contribution from two-particle higher-twist contributions is of great importance and the uncertainties are dominated by the inverse moment of $phi_D^+(omega, mu)$. With the obtained form factors, the predicted Cabibbo-Kobayashi-Maskawa (CKM) matrix elements are $|V_{cd}|=0.151,{}^{+0.091}_{-0.043} big |_{rm th.},{}^{+0.017}_{-0.02} big |_{rm exp.}$ and $|V_{cs}|=0.89,{}^{+0.467}_{-0.234} big |_{rm th.},{}^{+0.008}_{-0.008} big |_{rm exp.}$.
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