Dark Vector Mesons at LHC Forward Detector Searches

Confining gauge dynamics in dark sector is promising to provide dark matter with a mass in the range of sub-GeV to GeV. These dark sectors consist of composite particles, such as dark baryons and dark mesons, that are neutral under the standard-model charge. Dark photon is introduced as a portal matter between the dark sector and the standard-model sector in order to alleviate cosmological problems, and dark hadrons are produced through the same dark photon at accelerator-based experiments. As dark vector mesons and dark pions have the similar masses, dark vector mesons can be long-lived particles, which will be explored by far-detector experiments. In this study, we study the future prospect of the LHC forward-detector experiments, FASER2 and FACET, for exploring the dark vector mesons. When dark photon is heavier than dark pions, the LHC forward-detector searches can be comparable to DarkQuest, and the invisible decay searches of dark photons can also explore the same parameter space. Meanwhile, when dark photon is lightest in the dark sector, their future prospect will be comparable to the visible decay searches for dark photons at LHCb, Belle-II, and HPS.