  We consider the dipole portal to sterile neutrinos, also called heavy neutral
leptons (HNLs). The dipole interaction with the photon leads to HNL production
in meson decays, as well as triggers the HNL decay into an active neutrino and
a photon. HNLs with masses of order of 0.01-1 GeV are naturally long-lived if
the dipole coupling is sufficiently small. We perform Monte-Carlo simulations
and derive the sensitivities of the proposed FASER2 and FACET long-lived
particle experiments to HNLs produced via the dipole operator in meson decays
at the high-luminosity LHC. Our findings show that these future detectors will
be complementary to each other, as well as to existing experiments, and will be
able to probe new parts of the parameter space, especially in the case of the
dipole operator coupled to the tau neutrino.
