B → Dℓν ℓ form factors beyond leading power and extraction of |V cb | and R ( D )

We investigate the subleading-power corrections to the exclusive B → Dℓν ℓ form factors at 𝒪 ( α_s^0 ) in the light-cone sum rules (LCSR) framework by including the two- and three-particle higher-twist contributions from the B -meson light-cone distribution amplitudes up to the twist-six accuracy, by taking into account the subleading terms in expanding the hard-collinear charm-quark propagator, and by evaluating the hadronic matrix element of the subleading effective current . Employing further the available leading-power results for the semileptonic B → D form factors at the next-to- leading-logarithmic level and combining our improved LCSR predictions with the recent lattice determinations, we then carry out a comprehensive phenomenological analysis on the semi-leptonic B → Dℓν ℓ decay. We extract |V_cb|=(40.2_-0.5^+0.6|_th_-1.4^+1.4|_exp)×10^-3(|V_cb|=(40.9_-0.5^+0.6|_th_-1.0^+1.0|_exp)×10^-3) using the BaBar (Belle) experimental data, and particularly obtain for the gold-plated ratio R ( D ) = 0 . 302 ± 0 . 003.