Study of b⟶c Induced B�∗ ⟶Vℓν�ℓ Decays

In this paper, we investigate the tree-dominated B�∗
u,d,s,c⟶Vℓ−ν�ℓ (V = D∗
u,d, D∗
s , J/ψ and ℓ = e, μ, τ) decays in the Standard Model
with the relevant form factors obtained in the light-front quark model. These decays involve much more helicity states relative to
the corresponding B�∗⟶Pℓ−ν�ℓ and B�⟶Vℓ−ν�ℓ decays, and moreover, the contribution of longitudinal polarization mode (V
meson) is relatively small, ~ 30%, compared with the corresponding B meson decays. We have also computed the branching
fraction, lepton spin asymmetry, forward-backward asymmetry, and ratio R∗ðLÞ
V ≡ BðB�∗⟶Vτ−ν�τÞ/BðB�∗⟶Vℓ′−ν�ℓ′Þðℓ′ = e,
μÞ. Numerically, the branching fractions of B�∗⟶Vℓ′−ν�ℓ′ decays are at the level of Oð10−7Þ and are hopeful to be observed by
LHC and Belle-II experiments. The ratios R∗ðLÞ
D∗,D∗
s ,J/ψ have relatively small theoretical uncertainties and are close to each other,
R∗ðLÞ
D∗ ≃ R∗ðLÞ
D∗
s ≃ R∗ðLÞ
J/ψ ≃ ½0:26,0:27ð½0:27,0:29Þ, which are a bit different from the predictions in some previous works. The future
measurements are expected to make tests on these predictions.