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We evaluate long-distance electromagnetic (QED) contributions to $bar{B}{}^0 to D^+ tau^{-} bar{ u}_{tau}$ and $B^- to D^0 tau^{-} bar{ u}_{tau}$ relative to $bar{B}{}^0 to D^+ mu^{-} bar{ u}_{mu}$ and $B^- to D^0 mu^{-} bar{ u}_{mu}$, respectively, in the standard model. We point out that the QED corrections to the ratios $R(D^{+})$ and $R(D^{0})$ are not negligible, contrary to the expectation that radiative corrections are almost canceled out in the ratio of the two branching fractions. The reason is that long-distance QED corrections depend on the masses and relative velocities of the daughter particles. We find that theoretical predictions for $R(D^{+})^{tau/mu}$ and $R(D^{0})^{tau/mu}$ can be amplified by $sim4%$ and $sim3%$, respectively, for the soft-photon energy cut in range $20$-$40$ MeV.
We study potential New Physics effects in the $bar B to D^{(*)} tau bar u$ decays. As a particular example of New Physics models we consider the class of leptoquark models and put the constraints on the leptoquark couplings using the recently measure
At present, the measurements of $R_{D^{(*)}}$ and $R_{J/psi}$ hint at new physics (NP) in $b to c tau^- {bar u}$ decays. The angular distribution of ${bar B} to D^* (to D pi) , tau^{-} {bar u}_tau$ would be useful for getting information about the NP
We report a measurement of the branching fraction ratios R(D(*)) of Bbar -> D(*) tau- nubar_tau relative to Bbar -> D()* l- nubar_l (where l = e or mu) using the full Belle data sample of 772 x 10^6 BBbar pairs collected at the Y(4S) resonance with t
We report a measurement of ratio ${cal R}(D^*) = {cal B}(bar{B}^0 rightarrow D^{*+} tau^- bar{ u}_{tau})/{cal B}(bar{B}^0 rightarrow D^{*+} ell^- bar{ u}_{ell})$, where $ell$ denotes an electron or a muon. The results are based on a data sample conta
We report a measurement of the ratio ${cal R}(D^*) = {cal B}(bar{B}^0 rightarrow D^{*+} tau^- bar{ u}_{tau})/{cal B}(bar{B}^0 rightarrow D^{*+} ell^- bar{ u}_{ell})$, where $ell$ denotes an electron or a muon. The results are based on a data sample c