Probing the effects of new physics in ${\bar{B}}^{\ast }\to P\ell {\bar{\nu }}_{\ell }$ decays

Abstract

The significant divergence between the SM predictions and experimental measurements for the ratios, $R_{D^{(\ast )}}\equiv \mathcal{B}(\bar{B}\to D^{(\ast )}{\tau }^{-}{\bar{\nu }}_{\tau })/\mathcal{B}(\bar{B}\to D^{(\ast )}{\ell }^{\prime -}{\bar{\nu }}_{{\ell }^{\prime }})$ with $({\ell }^{\prime }=e,\mu )$, implies possible hint of new physics in the flavour sector. In this paper, motivated by the "$R_{D^{(\ast )}}$ puzzle" and abundant $B^{\ast }$ data samples at high-luminosity heavy-flavor experiments in the future, we try to probe possible effects of new physics in the semileptonic ${\bar{B}}_{u,d,s}^{\ast }\to P{\ell }^{-}{\bar{\nu }}_{\ell }$ $(P=D,D_s,\pi ,K)$ decays induced by $b\to (u,c){\ell }^{-}{\bar{\nu }}_{\ell }$ transitions in the model-independent vector and scalar scenarios. Using the spaces of NP parameters obtained by fitting to the data of $R_D$ and $R_{D^{\ast }}$, the NP effects on the observables including branching fraction, ratio $R_P^{\ast }$, lepton spin asymmetry and lepton forward-backward asymmetry are studied in detail. We find that the vector type couplings have large effects on the branching fraction and ratio $R_P^{\ast }$. Meanwhile, the scalar type couplings provide significant contributions to all of the observables. The future measurements of these observables in the ${\bar{B}}^{\ast }\to P{\ell }^{-}{\bar{\nu }}_{\ell }$ decays at the LHCb and Belle-II could provide a way to crosscheck the various NP solutions to the "$R_{D^{(\ast )}}$ puzzle".

24 pages, 4 figures