Probing New Physics with $q^2$ distributions in $bar{B} to D^{(*)} tau bar u$

Recent experimental results for the ratios of the branching fractions of the decays $bar{B} to D^{(*)} tau bar u$ and $bar{B} to D^{(*)} mu bar u$ came as a surprise and lead to a discussion of possibility of testing New Physics beyond the Standard Model through these modes. We show that these decay channels can provide us with good constraints on New Physics and several New Physics cases are favored by the present experimental data. In order to discriminate various New Physics scenarios, we examine the $q^2$ distributions and estimate the sensitivity of this potential measurement at the SuperKEKB/Belle II experiment.

Testing leptoquark models in $bar B to D^{(*)} tau bar u$

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 measured ratios $R(D^{(*)})=BR(bar B to D^{(*)} tau bar u)/BR(bar B to D^{(*)} mu bar u)$. For consistency, some of the constraints are compared with the ones coming from the current experimental bound on $BR(B to X_s u bar u)$. In order to discriminate various New Physics scenarios, we examine the correlations between different observables that can be measured in future.