Search for a Doubly Charged Scalar at the LHC and FCC-hh

Abstract: Doubly charged scalars frequently emerge in many well-motivated extensions of the Standard Model, particularly in frameworks that aim to explain the origin of neutrino masses. Their distinct electric charge and clean leptonic signatures make them especially compelling from the standpoint of experimental searches. In this work, we explore the sensitivity of the LHC full run II, including photon-photon fusion, and Future Circular Collider in its hadron-hadron configuration (FCC-hh) to such states, assuming they decay promptly and exclusively into charged leptons either conserving or violating lepton flavor. We find that the FCC-hh, operating at 100 TeV, is uniquely positioned to probe doubly charged scalars with masses up to 7 TeV and possibly establish the mechanism behind neutrino masses.