  We explore long-lived particle (LLP) searches using non-pointing photons at
the LHC as a probe for sterile-to-sterile and active-to-sterile transition
magnetic dipole moments of sterile neutrinos. We consider heavy sterile
neutrinos with masses ranging from a few~GeV to several hundreds of GeV. We
discuss transition magnetic dipole moments using the Standard Model effective
field theory and low-energy effective field theory extended by sterile
neutrinos ($N_R$SMEFT and $N_R$LEFT) and also provide a simplified UV complete
model example. LLP searches at the LHC using non-pointing photons will probe
sterile-to-sterile dipole moments two orders of magnitude below the current
best constraints from LEP, while an unprecedented sensitivity to sterile
neutrino mass of about 700 GeV is expected for active-to-sterile dipole
moments. For the UV-model example with one-loop transition magnetic moments,
the searches for charged lepton flavour violating processes in synergy with LLP
searches at the LHC can probe new physics at several TeV mass scales and
provide valuable insights into the lepton flavour structure of new physics
couplings.
