Heavy Neutrinos at the FCC-hh in the $U(1)_{B-L}$ Model

We investigate the potential of the 100 TeV future circular collider (FCC-hh) to probe heavy neutrinos. We concentrate in particular on heavy neutrino production via a $U(1)_{B-L}$ $Z'$ gauge boson and contrast the resulting limits with that mediated by Standard Model weak currents. We consider heavy neutrino decays to semi-leptonic as well as fully leptonic final states, particularly with muon flavour, and we show the importance of considering searches both in prompt and displaced decays of the heavy neutrinos. For prompt final states, semi-leptonic modes are more promising due to smaller background and larger yields, and TeV-scale heavy neutrinos with active-sterile mixing compatible with light neutrino mass generation in a seesaw scenario can be probed for a 5 TeV $Z'$ and gauge coupling as low as $g_{B-L} = 10^{-2}$. Displaced vertex searches can extend this range to heavy neutrino masses as low as 10 GeV.