$B to pi ell u_l$ Width and $|V_{ub}|$ from QCD Light-Cone Sum Rules

We employ the $Btopi$ form factors obtained from QCD light-cone sum rules and calculate the $Bto pi ell u_l$ width ($ell=e,mu$) in units of $1/|V_{ub}|^2$, integrated over the region of accessible momentum transfers, $0leq q^2leq 12.0 ~GeV^2$. Using the most recent BABAR-collaboration measurements we extract $|V_{ub}|=(3.50^{+0.38}_{-0.33}big|_{th.}pm 0.11 big|_{exp.})times 10^{-3}$. The sum rule results for the form factors, taken as an input for a $z$-series parameterization, yield the $q^2$-shape in the whole semileptonic region of $Bto piell u_ell$. We also present the charged lepton energy spectrum in this decay. Furthermore, the current situation with $Bto tau u_tau$ is discussed from the QCD point of view. We suggest to use the ratio of the $Bto pi tau u_tau$ and $Bto piell u_l ~(ell =mu,e) $ widths as an additional test of Standard Model. The sensitivity of this observable to new physics is illustrated by including a charged Higgs-boson contribution in the semileptonic decay amplitude.

Semileptonic charm decays $D to pi l u_{l}$ and $D to K l u_l$ from QCD Light-Cone Sum Rules

We present a new calculation of the $Dtopi$ and $D to K$ form factors from QCD light-cone sum rules. The $overline{MS}$ scheme for the $c$-quark mass is used and the input parameters are updated. The results are $f^+_{Dpi}(0)= 0.67^{+0.10}_{-0.07}$, $f^+_{DK}(0)=0.75^{+0.11}_{-0.08}$ and $f^+_{Dpi}(0)/f^+_{DK}(0)=0.88 pm 0.05$. Combining the calculated form factors with the latest CLEO data, we obtain $|V_{cd}|=0.225pm 0.005 pm 0.003 ^{+0.016}_{-0.012}$ and $|V_{cd}|/|V_{cs}|= 0.236pm 0.006pm 0.003pm 0.013$ where the first and second errors are of experimental origin and the third error is due to the estimated uncertainties of our calculation. We also evaluate the form factors $f^-_{Dpi}$ and $f^-_{DK}$ and predict the slope parameters at $q^2=0$. Furthermore, calculating the form factors from the sum rules at $q^2<0$, we fit them to various parameterizations. After analytic continuation, the shape of the $Dto pi,K $ form factors in the whole semileptonic region is reproduced, in a good agreement with experiment.

Light-cone sum rules for $B to pi$ form factors revisited

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.