Using the formulas for the $d\Gamma / dq^2$ distribution with non-zero lepton mass and experimentally determined form factors, we calculate the $d\Gamma (D^{ (*)+} l^- { \bar{ \nu}})/ dq^2$ spectra and branching fractions for $l=e$, $\mu$ and $\tau$. We obtain the results ${ \cal{ B}}({ \bar{ B}}^0\rightarrow D^{ +} \tau^- { \bar{ \nu}})/ { \cal{ B}}({ \bar{ B}}^0\rightarrow D^{ +} e^- { \bar{ \nu}})= 0.278^{ +0.049}_{ -0.035}$ and ${ \cal{ B}}({ \bar{ B}}^0\rightarrow D^{ *+} \tau^- { \bar{ \nu}})/ { \cal{ B}}({ \bar{ B}}^0\rightarrow D^{ *+} e^- { \bar{ \nu}})= 0.256^{ +0.014}_{ -0.013}$ . Since we used the experimentally measured form factors, these results are independent of theoretical models of form factors.
Categories: hep-ph