Probing TeV-scale Majorana neutrinos at a muon-proton collider via a lepton-number-violating fat-jet signature

We investigate the sensitivity to TeV-scale heavy Majorana neutrinos at a future muon-proton collider with √s=5.3 s = 5.3 TeV, based on 1 TeV muon and 7 TeV proton beams. We focus on the lepton-number-violating (LNV) process μ ⁻ p → jN μ - p → j N , followed by N→ μ ⁺W⁻→ μ ⁺J N → μ + W - → μ + J , leading to the characteristic final state jμ ⁺J j μ + J . Here, j denotes the associated light jet from heavy-neutrino production, while J denotes the fat jet originating from the hadronic d ecay of the highly boosted W boson. This topology provides a clean experimental signature with strongly suppressed Standard Model backgrounds. A comprehensive signal and background analysis is performed using parton showering, fast detector simulation, and dedicated fat-jet reconstruction. We derive the projected 2σ 2 σ exclusion limits on the muon-flavor mixing parameter |Vμ N|² | V μ N | 2 for integrated luminosities of 100 fb ⁻¹ - 1 and 1 ab ⁻¹ - 1 . For heavy-neutrino masses in the range 1~TeV≤ mN≤ 3~TeV 1 TeV ≤ m N ≤ 3 TeV , the projected upper limits on |Vμ N|² | V μ N | 2 range from