Semileptonic ${\bar{B}}_c^{\ast }\to (P,V){\mathrm{\ell }}^{-}{\bar{\nu }}_{\mathrm{\ell }}$ decays within the self-consistent light-front quark model

Motivated by the recent observation of the $B_c^{\ast }$ meson by the ATLAS Collaboration and its promising discovery potential at future high-luminosity colliders, we investigate the semileptonic decays ${\bar{B}}_c^{\ast }\to (P,V){\mathrm{\ell }}^{-}{\bar{\nu }}_{\mathrm{\ell }}$ ($P=D$, $B_{d,s}$, ${\eta }_c(1S,2S,3S)$; $V=D^{\ast }$, $B_{d,s}^{\ast }$, $\psi (1S,2S,3S)$) in the Standard Model. Using the relevant form factors obtained in the self-consistent covariant light-front quark model, we present theoretical predictions for several physical observables, including the branching fraction, the ratios of branching fractions $R_{(L)}$, the longitudinal polarization fraction of the daughter vector meson, the $\tau$ lepton spin asymmetry and the forward-backward asymmetry. It is found that the branching fractions for the Cabibbo-favored ${\bar{B}}_c^{\ast }$ $\to$ ${\bar{B}}_s^{\ast }{e}^{-}{\bar{\nu }}_e$ and ${\bar{B}}_s^{\ast }{\mu }^{-}{\bar{\nu }}_{\mu }$ decays reach the order of $\mathcal{O}({10}^{-6})$, which might be firstly observed at the future high-luminosity Large Hadron Collider.