Updated light-cone sum rule form factors for B(s), D(s) to eta(eta') are fitted across the full q^2 range and used to extract V_ub, V_cs and V_cd with precision the authors call comparable to standard analyses.
$B \to \pi \ell \nu_l$ Width and $|V_{ub}|$ from QCD Light-Cone Sum Rules
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abstract
We employ the $B\to\pi$ form factors obtained from QCD light-cone sum rules and calculate the $B\to \pi \ell \nu_l$ width ($\ell=e,\mu$) in units of $1/|V_{ub}|^2$, integrated over the region of accessible momentum transfers, $0\leq q^2\leq 12.0 ~GeV^2$. 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 $B\to \pi\ell\nu_\ell$. We also present the charged lepton energy spectrum in this decay. Furthermore, the current situation with $B\to \tau\nu_\tau$ is discussed from the QCD point of view. We suggest to use the ratio of the $B\to \pi \tau\nu_\tau$ and $B\to \pi\ell \nu_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.
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Form factors and phenomenology of $\boldsymbol{B_{(s)}}$ and $\boldsymbol{D_{(s)}}$ semileptonic decays to $\boldsymbol{\eta}$ and $\boldsymbol{\eta^\prime}$
Updated light-cone sum rule form factors for B(s), D(s) to eta(eta') are fitted across the full q^2 range and used to extract V_ub, V_cs and V_cd with precision the authors call comparable to standard analyses.