Precision calculations of $B \to V$ form factors in QCD

Understand

Applying the vacuum-to-$B$-meson correlation functions with an interpolating current for the light vector meson we construct the light-cone sum rules (LCSR) for the "effective" form factors $\xi_{\parallel}(n \cdot p)$, $\xi_{\perp}(n \cdot p)$, $\Xi_{\parallel}(\tau, n \cdot p)$ and $\Xi_{\perp}(\tau, n \cdot p)$, defined by the corresponding hadronic matrix elements in soft-collinear effective theory (SCET), entering the leading-power factorization formulae for QCD form factors responsible for $B \to V \ell \bar \nu_{\ell}$ and $B \to V \ell \bar \ell$ decays at large hadronic recoil at next-to-leading-order in QCD.

• The light-quark mass effect for the local SCET form factors $\xi_{\parallel}(n \cdot p)$ and $\xi_{\perp}(n \cdot p)$ is also computed from the LCSR method with the $B$-meson light-cone distribution amplitude $\phi_B^{+}(\omega, \mu)$ at ${\cal O}(\alpha_s)$.
• Furthermore, the subleading power corrections to $B \to V$ form factors from the higher-twist $B$-meson light-cone distribution amplitudes are also computed with the same method at tree level up to the twist-six accuracy.
• Having at our disposal the LCSR predictions for $B \to V$ form factors, we further perform new determinations of the CKM matrix element $|V_{ub}|$ from the semileptonic $B \to \rho \, \ell \, \bar \nu_{\ell}$ and $B \to \omega \, \ell \, \bar \nu_{\ell}$ decays, and predict the normalized differential branching fractions and the $q^2$-binned $K^{\ast}$ longitudinal polarization fractions of the exclusive rare $B \to K^{\ast} \, \nu_{\ell} \, \bar \nu_{\ell}$ decays.