A massive right-handed sterile neutrino in three-body $\bar{B}\to D^{\ast }{\mathrm{\ell }}^{-}{\bar{N}}_R$ decays - a Monte Carlo simulation study

We investigate the differential decay distributions of $\bar{B}\to D^{\ast }{\mathrm{\ell }}^{-}{\bar{N}}_R$, where $N_R$ is a heavy right-handed neutrino (RHN) and $\mathrm{\ell }=e,\mu$. We employ a newly developed Monte Carlo event generator based on the EvtGen framework that can simulate beyond-the-Standard-Model processes. We validate the implementation of the model by comparing the Monte-Carlo results with analytical results for several kinematic variables such as $q^2$ and missing mass, as well as signatures in the angular distributions such as $A_{FB}$, $S_3$, $S_5$, etc. This MC Generator will enable new experimental searches for RHNs. We discuss the sensitivity of various observables to the presence of an RHN and the feasibility of an experimental analysis at Belle II.