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Register a new userLight-Cone Sum Rules for $Bto Kpi$ Form Factors and Applications to Rare Decays
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We derive a set of light-cone sum rules relating the hadronic form factors relevant for $Bto Kpiell^+ell^-$ decays to the $B$-meson light-cone distribution amplitudes (LCDAs). We obtain the sum rule relations for all $Bto Kpi$ form factors of (axial)vector and (pseudo)tensor $bto s$ currents with a $P$-wave $Kpi$ system. Our results reduce to the known light-cone sum rules for $Bto K^*$ form factors in the limit of a single narrow-width resonance. We update the operator-product expansion for the underlying correlation function by including a more complete set of $B$-meson LCDAs with higher twists, and produce numerical results for all $Bto K^*$ form factors in the narrow-width limit. We then use the new sum rules to estimate the effect of a non-vanishing $K^*$ width in $Bto K^*$ transitions, and find that this effect is universal and increases the factorizable part of the rate of $Bto K^*X$ decays by a factor of $20%$. This effect, by itself, goes in the direction of increasing the current tension in the differential $Bto K^*mumu$ branching fractions. We also discuss $Bto Kpi$ transitions outside the $K^*$ window, and explain how measurements of $Bto Kpiellell$ observables above the $K^*$ region can be used to further constrain the $Bto K^*$ form factors.
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The form factors of the semileptonic $Bto pipiellbar u$ decay are calculated from QCD light-cone sum rules with the distribution amplitudes of dipion states. This method is valid in the kinematical region, where the hadronic dipion state has a small invariant mass and simultaneously a large recoil. The derivation of the sum rules is complicated by the presence of an additional variable related to the angle between the two pions. In particular, we realize that not all invariant amplitudes in the underlying correlation function can be used, some of them generating kinematical singularities in the dispersion relation. The two sum rules that are free from these ambiguities are obtained in the leading twist-2 approximation, predicting the $bar{B}^0to pi^+pi^0$ form factors $F_{perp}$ and $F_{parallel}$ of the vector and axial $bto u$ current, respectively. We calculate these form factors at the momentum transfers $0<q^2lesssim 12 $ GeV$^2$ and at the dipion mass close to the threshold $4m_pi^2$. The sum rule results indicate that the contributions of the higher partial waves to the form factors are suppressed with respect to the lowest $P$-wave contribution and that the latter is not completely saturated by the $rho$-meson term.
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.
Form factors of the rare $Lambda_{b}(Lambda_{b}^*)to Nell^{+}ell^{-}$ decays are calculated in the framework of the light cone QCD sum rules by taking into account of the contributions from the negative parity baryons. Using the obtained results on the form factors, the branching ratios of the considered decays are estimated. The numerical survey for the branching ratios of the $Lambda_b rar Nell^+ell^- $ and $Lambda_b^ast rar Nell^+ell^- $ decays indicate that these transitions could be measurable in LHCb in near future. Comparison of our predictions on the form factors and branching ratios with those existing in the literature is also performed.
We study the electromagnetic nucleon form factors within the approach based on light-cone sum rules. We include the next-to-leading-order corrections for the contributions of twist-three and twist-four operators and a consistent treatment of the nucleon mass corrections in our calculation. It turns out that a self-consistent picture arises when the three valence quarks carry $40%:30%:30%$ of the proton momentum.
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