Optimization of muon suppression using sweeper magnets for the Forward Physics Facility at the HL-LHC

Abstract: The Forward Physics Facility (FPF) at the High-Luminosity LHC (HL-LHC) will enable high-statistics measurements of TeV-scale neutrinos, but the intense flux of forward muons poses a major challenge for neutrino detectors in the far-forward region. We investigate the suppression of background muons using sweeper magnets with a simulation framework combining SIBYLL event generation, BDSIM beam transport, Geant4 particle tracking, and realistic magnetic field maps. Starting from a muon flux of $3.8\times10<sup>3~\mathrm{cm<sup>{-2}}$ per $\mathrm{fb<sup>{-1}}$ without magnets, a magnet in the LHC tunnel alone achieves the target level of $2\times10<sup>3~\mathrm{cm<sup>{-2}}$ per $\mathrm{fb<sup>{-1}}$. Additional magnets at the TI18 tunnel and FPF entrance further reduce the flux to $1.5\times10<sup>3~\mathrm{cm<sup>{-2}}$ per $\mathrm{fb<sup>{-1}}$ in the optimized configuration. These results demonstrate that a properly optimized multi-stage sweeper magnet system can significantly reduce the forward muon background, while also highlighting the importance of realistic transport simulations and geometrical constraints in achieving further suppression.