Symmetries in $B \to D^* \ell \nu$ angular observables

Understand

We apply the formalism of amplitude symmetries to the angular distribution of the decays $B \to D^* \ell \nu$ for $\ell=e,\mu,\tau$.

• We show that the angular observables used to describe the distribution of this class of decays are not independent in absence of New Physics contributing to tensor operators.
• We derive sets of relations among the angular coefficients of the decay distribution for the massless and massive lepton cases which can be used to probe in a very general way the consistency among the angular observables and the underlying New Physics at work.
• We use these relations to access the longitudinal polarisation fraction of the $D^*$ using different angular coefficients from the ones used by Belle experiment.