Semitauonic B decays at Belle/Belle II

Abstract

It is experimentally observed that ratios of branching fractions for semitauonic and semileptonic $B$ decays, known as the $R(D^{(*)})$, are higher than Standard Model (SM) predictions. The $B \to \bar{D}^{(*)} \tau^{+} \nu_{\tau}$ decays, except for the branching fractions, offer also other observables, in particular, angular observables may determine spin structure of a potential New Physics (NP) providing some clues to explain the $R(D^{(*)})$ puzzle. In this review, polarization measurements in $B \to \bar{D}^{*} \tau^{+} \nu_{\tau}$ decays at Belle are presented and prospects for measurements of characteristics of semitauonic $B$ decays at Belle/Belle II are described.