Massive right-handed neutrinos in $\bar{B} \to D^* \tau \bar X$ decay

Abstract

We explore signatures of a massive right-handed neutrino (RHN) in angular distributions of $\bar{B} \to D^* (\to D \pi) \tau (\to \pi \nu_\tau ) \bar X$ decays, where $X$ is an invisible state. We assume the new physics is described by the standard model effective field theory extended with an RHN in the MeV-GeV mass range. We calculate for the first time the full differential distributions in terms of the visible final states, including the decay of the $\tau$ lepton. We evaluate the sensitivity of various distributions to the new physics operators.