Fat jet signature of a heavy neutrino at a lepton collider

We explore the discovery prospect of a very heavy neutrino at the proposed e⁺e^- collider for two different c.m. energies √s=1.4 and 3 TeV. We consider production of a heavy neutrino via s- and t-channel processes and its subsequent prompt decays leading to semileptonic final states, along with significant missing momentum. For our choice of masses, the gauge boson produced from heavy neutrino decay is highly boosted, leading to a fat jet. We carry out a detailed signal and background analysis for e^±+jfat+)p̄ (missing four-momentum) final state using both cut-based and multivariate techniques. We show that a heavy neutrino of mass 600--2700 GeV and active-sterile mixing |VeN|²~10^-5 can be probed with 5σ significance at an e⁺e^- collider after collecting L=500 fb^-1 of data. We find that the sensitivity reach at an e⁺e^- collider is an order of magnitude enhanced compared to the LHC.