Cerci, S.Işıldak, Bora2023-06-222023-06-222022-06-201029-8479http://hdl.handle.net/10679/8463https://doi.org/10.1007/JHEP06(2022)110We describe a proposal to add a set of very forward detectors to the CMS experiment for the high-luminosity era of the Large Hadron Collider to search for beyond the standard model long-lived particles, such as dark photons, heavy neutral leptons, axion-like particles, and dark Higgs bosons. The proposed subsystem is called FACET for Forward-Aperture CMS ExTension, and will be sensitive to any particles that can penetrate at least 50 m of magnetized iron and decay in an 18 m long, 1 m diameter vacuum pipe. The decay products will be measured in detectors using identical technology to the planned CMS Phase-2 upgrade.engopenAccesshttps://creativecommons.org/licenses/by/4.0/article2022600081424930000210.1007/JHEP06(2022)110Beyond standard modelDark matterExoticsHadron-hadron scatteringParticle and resonance production2-s2.0-85132165196