Study of sub-GeV dipolar dark states at SND@LHC within invisible bounds on meson decays

Electromagnetic form factors constitute a natural portal for accessing states beyond the Standard Model. In particular, dimension-5 magnetic and electric dipole moment operators offer a minimal and predictive framework for Feebly Interacting Particles (FIPs). In this work, we study the sensitivity of the Scattering and Neutrino Detector (SND@LHC) to dipolar dark states through photon-mediated interactions with Standard Model particles. The far-forward region of the LHC provides FIPs with large momenta that scatter off electrons and nuclei inside the target. The production of dark states from meson decays is constrained by invisible decay widths, while the Drell-Yan process offers a production channel in the GeV range. We derive projected sensitivity limits for magnetic and electric dipole moment interactions at SND@LHC under conservative assumptions and compare them with constraints from direct detection, beam-dump, fixed-target, and collider experiments. We also assess the validity of the effective field theory description by considering conservative bounds on the couplings.