First Physics Results from the FASER Experiment

Abstract

FASER is a new 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 physics results from the initial year of data-taking are presented. A search for dark photons decaying to an electron-positron pair found no events, yielding new constraints on dark photons with couplings $ε\sim 10^{-5} - 10^{-4}$ and masses $\sim 10$ MeV $- 100$ MeV. A search for muon-neutrino charged-current interactions in a tungsten target at the front of the FASER experiment found $153^{+12}_{-13}$ neutrino candidates with a negligible background. The reconstructed charge and momentum distributions imply the observation of both neutrinos and anti-neutrinos with an incident neutrino energy above 200 GeV.