Considering the nonfactorizable QED corrections, the branching ratios and ratios of branching ratios $R(D_{ s}^{ ({ \ast})})$ for the semileptonic $\overline{ B}_{ s}$ ${ \to}$ $D_{ s}^{ (\ast)} { \ell} \bar{ \nu}_{ \ell}$ decays are reevaluated. It is found that (a) the QED contributions can enhance the branching ratios and reduce the ratios $R(D_{ s}^{ ({ \ast})})$. (b) The $SU(3)$ flavor symmetry holds basically well in the ratios $R(D)$-$R(D^{ \ast})$ for the semileptonic charmed $\overline{ B}_{ u,d,s}$ decays. (c) The current theoretical uncertainties of branching ratios ${ \cal B}(\overline{ B}_{ s} { \to} D_{ s}^{ \ast} { \ell} \bar{ \nu}_{ \ell})$ from the form factors are very large.
Categories: hep-ph hep-ex