First Results from the Search for Dark Photons with the FASER Detector at the LHC

FASER is an LHC experiment designed to search for light, weakly-interacting particles that are produced in proton-proton collisions at the ATLAS interaction point and travel in the far-forward direction. The first results from a search for dark photons decaying to an electron-positron pair, using a dataset corresponding to an integrated luminosity of 27.0 fb$^{-1}$ collected at center-of-mass energy $\sqrt{s} = 13.6$ TeV in 2022 in LHC Run 3, are presented. No events are seen in an almost background-free analysis, yielding world-leading constraints on dark photons with couplings $\epsilon \sim 10^{-5} - 10^{-4}$ and masses $\sim 10$ MeV - $100$ MeV.