Charged and neutral (B)over-baru,d,s → γ form factors from light cone sum rules at NLO

We present the first analytic O(alpha(s))-computation at twist-1,2 of the (B) over bar (u,d,s) -> gamma form factors within the framework of sum rules on the light-cone. These form factors describe the charged decay (B) over bar (u) -> gamma l(-)(nu) over bar, contribute to the flavour changing neutral currents (B) over bar (d,s) -> gamma l(+)l(-) and serve as inputs to more complicated processes. We provide a fit in terms of a z-expansion with correlation matrix and extrapolate the form factors to the kinematic endpoint by using the g(BB*gamma) couplings as a constraint. Analytic results are available in terms of multiple polylogarithms in the supplementary material. We give binned predictions for the (B) over bar (u) -> gamma l(-)(nu) over bar branching ratio along with the associated correlation matrix. By comparing with three SCET-computations we extract the inverse moment B-meson distribution amplitude parameter lambda(B) = 360(110) MeV. The uncertainty thereof could be improved by a more dedicated analysis. In passing, we extend the photon distribution amplitude to include quark mass corrections with a prescription for the magnetic vacuum susceptibility, chi(q), compatible with the twist-expansion. The values chi(q) = 3.21(15) GeV-2 and chi(s) = 3.79(17) GeV-2 are obtained.