Testing leptogenesis and seesaw in the B-L model using long-lived particle searches

We discuss the potential of using long-lived particle (LLP) searches for right-handed neutrinos (RHNs) to test resonant leptogenesis and the seesaw mechanism. This is challenging if only RHNs are added to the Standard Model, as naturally the active-sterile mixing strengths |VℓN|2 are small, for 1 GeV≲MN≲1000 GeV. Instead, we consider the minimal B-L gauge model, where a Z′ gauge boson couples to fermions including the RHNs. During leptogenesis, this gauge coupling introduces scattering processes that washout the B-L asymmetry. At colliders, it can lead to abundant production of RHNs which allows probing the associated seesaw mechanism using LLP searches. We find that LLP searches at the FCC-hh can test leptogenesis and the seesaw mechanism simultaneously and probe the active-sterile mixing at or below the seesaw floor.