Search for heavy Majorana neutrinos at muon-proton colliders via lepton-number-violating signals

Abstract

We propose a novel search strategy for heavy Majorana neutrinos based on the lepton-number-violating process ${\mu }^{-}p\to jN\to j({\ell }^{+}{W}^{-})$ at future muon-proton ($\mu p$) colliders equipped with 1 TeV muon beams and 7 TeV proton beams, yielding a center-of-mass energy of approximately 5.3 TeV. For heavy neutrinos with masses in the range $200\text{GeV}\lesssim m_N\lesssim 1000\text{GeV}$, this analysis targets the decay chain $N\to {\ell }^{+}{W}^{-}\to {\ell }^{+}jj$, producing a characteristic final state consisting of one charged lepton and three well-resolved jets. For TeV-scale Majorana neutrinos, the $W$ boson is highly boosted, such that its hadronic decay products coalesce into a prominent fat-jet ($J$) signature. We conduct comprehensive signal and background analyses that account for realistic detector effects to assess the search sensitivity. We derive the projected $2\sigma$ exclusion limits on the neutrino mixing parameter $|V_{\ell N}{|}^2$ based on two typical integrated luminosity scenarios of $100{\text{fb}}^{-1}$ and $1{\text{ab}}^{-1}$. The results demonstrate that the proposed search strategy can achieve constraints substantially superior to the existing bounds from the LHC and other high-energy colliders. This study demonstrates that future $\mu p$ colliders can provide competitive sensitivity for probing heavy Majorana neutrinos over the mass range $200\text{GeV}\le m_N\le 3000\text{GeV}$.

Comments: This work is withdrawn because our initial background simulation omitted collinear photon initial-state radiation off the muon beam. This missing background component invalidates the main sensitivity results. We will perform full corrected simulations and resubmit a revised study in the future