Abstract
We present a novel search strategy for heavy Majorana neutrinos in the context of the lepton-number-violating process e−p→jN→j(ℓ+W−) at future electron-proton (ep) colliders, including the Large Hadron electron Collider (LHeC) and the electron-hadron mode of the Future Circular Collider (FCC-eh). The analysis focuses on the decay chain N→ℓ+W−→ℓ+jj, which yields a distinctive final-state signature characterized by one charged lepton and three jets. We consider electron beams with an energy of 60 GeV and a maximum polarization of 80%, colliding with proton beams of 7 TeV (LHeC) and 50 TeV (FCC-eh), corresponding to centre-of-mass energies of approximately 1.3 and 3.5 TeV, and integrated luminosities of 1 and 3ab−1, respectively. Detailed signal-versus-background studies are performed with full detector simulation to quantify the sensitivity of the proposed search. Our results yield projected 2σ exclusion limits on the mixing parameter |VℓN|2, which significantly improve upon the current experimental constraints from the Large Hadron Collider (LHC) and other high-energy colliders. This work demonstrates that ep colliders provide the best achievable sensitivity for heavy neutrinos with masses below O(1TeV).