Physical review

FASER,the ForwArd Search ExpeRiment,is a proposed experiment dedicated to\nsearching for light, extremely weakly-interacting particles at the LHC. Such\nparticles may be produced in the LHC's high-energy collisions and travel long\ndistances through concrete and rock without interacting. They may then decay to\nvisible particles in FASER, which is placed 480 m downstream of the ATLAS\ninteraction point. In this work we briefly describe the FASER detector layout\nand the status of potential backgrounds. We then present the sensitivity reach\nfor FASER for a large number of long-lived particle models, updating previous\nresults to a uniform set of detector assumptions, and analyzing new models. In\nparticular, we consider all of the renormalizable portal interactions, leading\nto dark photons, dark Higgs bosons, and heavy neutral leptons (HNLs); light B-L\nand $L_i - L_j$ gauge bosons; axion-like particles (ALPs) that are coupled\ndominantly to photons, fermions, and gluons through non-renormalizable\noperators; and pseudoscalars with Yukawa-like couplings. We find that FASER and\nits follow-up, FASER 2, have a full physics program, with discovery sensitivity\nin all of these models and potentially far-reaching implications for particle\nphysics and cosmology.\n

FASER’s physics reach for long-lived particles