The FASER experiment at the LHC is designed to search for light, weakly-interacting particles produced in proton-proton collisions at the ATLAS interaction point that 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 $\epsilon \sim 2 \times 10^{ -5} - 1 \times 10^{ -4}$ and masses $\sim$ 17 MeV - 70 MeV. The analysis is also used to probe the parameter space of a massive gauge boson from a U(1)$_{ B-L}$ model, with couplings $g_{ B-L} \sim 5 \times 10^{ -6} - 2 \times 10^{ -5}$ and masses $\sim$ 15 MeV - 40 MeV excluded for the first time.
Categories: hep-ex hep-ph