Model Independent Calculation of ${\cal{B}}({\bar{B}}^0\to D^{(*)+} τ^- {\barν})/ {\cal{B}}({\bar{B}}^0\to D^{(*)+} e^- {\barν})$

Abstract

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