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Optimal-observable analysis of possible new physics in $B\to D^{(\ast)}τν_τ$

We study all possible observables in $B\to D^{(\ast)}τν_τ$ with new physics (NP), including new vector, scalar and tensor interactions, and investigate the prospects of extracting NP Wilson coefficients with optimal observables. Analysis of the full $q^2$ integrated branching fractions of $B\to D^{(\ast)}τν_τ$ show that the overall sensitivity of the observables of $B\to D τν_τ$ is more towards the scalar current, whereas the bin-by-bin analysis of $q^2$ distribution of the differential branching fraction points to regions of $q^2$ sensitive to tensor interactions. Interestingly, the observables in $B\to D^{\ast}τν_τ$ are more sensitive to tensor interactions, and bin-by-bin analysis of this mode shows the distinct regions of $q^2$ sensitive to vector or scalar interactions. In addition to that, the $τ$ polarisation asymmetry is found to be more sensitive to NP compared to the other observables, in both decay modes.