Speaker
Description
The observed small neutrino masses can be explained by type I seesaw models that predict the existence of heavy neutrinos. In a large part of the collider-accessible parameter space, these heavy neutral leptons would be long-lived and can be searched for with displaced vertex signatures. Additionally, collider-observable heavy neutrinos of type I seesaw models must form almost mass-degenerate pseudo-Dirac pairs as is for example captured by symmetry-protected seesaw models. Their tiny mass splitting induces heavy neutrino-antineutrino oscillations. We demonstrate the remarkable potential a Z-pole run of future lepton colliders such as the FCC-ee has to resolve these oscillations using angular distributions and displaced vertex signatures. Such a measurement would quantify the amount of lepton number violation present in the neutrino sector.
