Probing Light Muon-philic Scalars at Forward Detectors at LHC

The FASER experiment, located downstream of ATLAS interaction point, was conceived to study high energy collider neutrinos and other dark sector particles travelling in the forward direction. A main source of backgrounds in such studies are muons, and extensive effort is required to suppress them. In this study, we reverse this script and aim to use the muons produced in the direction of the FASER detector to search for new physics. We take the example of a light muon-philic scalar that could potentially explain the muon (g − 2) anomaly. Making use of new detector technologies that can differentiate two photons, we find that FASER, using just 2025 and Run 4 data, can probe some parts of the currently unconstrained regions of the parameter space that can explain the muon (g − 2) anomaly, and FASER2, proposed for the HL-LHC era, can completely cover this region.