Deep-inelastic scattering at TeV energies with LHC muons

The LHC far-forward experiments FASER and SND@LHC have pioneered the detection of TeV-energy neutrinos produced in hard-scattering proton-proton collisions at the LHC. In addition to neutrinos, an intense flux of TeV-energy muons reaches these detectors, representing a dominant background for both neutrino studies and beyond the Standard Model searches. Here we demonstrate that this forward muon flux enables a comprehensive neutral-current deep-inelastic scattering (DIS) program at FASER with a strong kinematical overlap with the Electron Ion Collider. For the Run 3 luminosity of L_pp=250 L pp = 250 fb ⁻¹, - 1 , more than 10⁵ 10 5 inclusive muon DIS events, of which up to 10⁴ 10 4 from charm production, are expected at FASER ν . ν . As a representative application, we demonstrate the sensitivity of muon DIS at FASER ν ν to probe the (intrinsic) charm content of the proton at large- x . We also provide predictions for event yields of muon DIS for future FASER runs and for the proposed Forward Physics Facility.