The form factors relevant to $B_{ q}\to D^{ \ast}_{ q}(J^{ P}=1^{ -}) ell\nu$ $(q=s, d, u)$ decays are calculated in the framework of the three point QCD sum rules approach. The heavy quark effective theory prediction of the form factors as well as $1/m_{ b}$ corrections to those form factors are obtained. A comparison of the results for the ratio of form factors at zero recoil limit and other values of $q^{ 2}$ with the predictions of the subleading Isgur-Wise form factor application for $B\to D^{ \ast}\ell\nu$ is presented. The total decay width and branching ratio for these decays are also evaluated using the $q^2$ dependencies of these form factors. The results are in good agreement with the constituent quark meson model and existing experimental data. The $q=s$ case can also be detected at LHC in the near future.
Categories: hep-ph