Probing sterile neutrinos in B

We present, how a systematic study of [Formula omitted] ( [Formula omitted]) decays with [Formula omitted], at Belle II (BESIII) can provide unambiguous signature of a heavy neutrino N and/or constrain its mixing with active neutrinos [Formula omitted], which is parameterized by [Formula omitted]. Our constraint on [Formula omitted] that can be achieved from the full Belle II data is comparable with what can be obtained from the much larger data set of the upgraded LHCb. Additionally, our method offers better constraint on [Formula omitted] for mass of sterile neutrino [Formula omitted] GeV. We can also probe the Dirac and Majorana nature of N by observing the sequential decay of N, including suppression from observation of a displaced vertex as well as helicity flip, for Majorana N.