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 $R(D^{(\ast )})$, are higher than Standard Model (SM) predictions. The $B\to {\bar{D}}^{(\ast )}{\tau }^{+}{\nu }_{\tau }$ 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 $R(D^{(\ast )})$ puzzle. In this review, polarization measurements in $B\to {\bar{D}}^{\ast }{\tau }^{+}{\nu }_{\tau }$ decays at Belle are presented and prospects for measurements of characteristics of semitauonic $B$ decays at Belle/Belle II are described.

arXiv comment5 pages, 3 figures, Proceedings of the 10th International Workshop on the CKM Unitarity Triangle (CKM 2018), Heidelberg, Germany, September 17-21, 2018; https://ckm2018.physi.uni-heidelberg.de/

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