Semileptonic decays $B\to D^{(\ast )}l\nu$ in the perturbative QCD factorization approach

Abstract

In this paper, we study the $B\to D^{(\ast )}{l}^{-}{\bar{\nu }}_{\mathrm{l}}$ semileptonic decays and calculate the branching ratios $\mathcal{B}(B\to D^{(\ast )}{l}^{-}{\bar{\nu }}_{\mathrm{l}})$ and the ratios $R(D^{(\ast )})$ and $R_{\mathrm{D}}^{\mathrm{l},\tau }$ by employing the perturbative QCD (pQCD) factorization approach. We find that (a) for $R(D)$ and $R(D^{\ast })$ ratios, the pQCD predictions are $R(D)=0.430_{-0.026}^{+0.021}$, $R(D^{\ast })=0.301\pm 0.013$ and agree well with BaBar's measurements of $R(D^{(\ast )})$; (b) for the newly defined $R_{\mathrm{D}}^{\mathrm{l}}$ and $R_{\mathrm{D}}^{\tau }$ ratios, the pQCD predictions are $R_{\mathrm{D}}^{\mathrm{l}}=0.450_{-0.051}^{+0.064}$ and $R_{\mathrm{D}}^{\tau }=0.642_{-0.070}^{+0.081}$, which may be more sensitive to the QCD dynamics of the considered semileptonic decays than $R(D^{(\ast )})$ and should be tested by experimental measurements.

Comments: 13 pages, 2 ps figures, 3 tables. Final version published in Chinese Science Bulletin