First Measurement of ν e and ν

The first results of the study of high-energy electron neutrino ( ν e ) and muon neutrino ( ν μ ) charged-current interactions in the FASER ν emulsion-tungsten detector of the FASER experiment at the LHC are presented. A 128.8 kg subset of the FASER ν volume was analyzed after exposure to 9.5     fb − 1 of s = 13.6     TeV p p data. Four (eight) ν e ( ν μ ) interaction candidate events are observed with a statistical significance of 5.2 σ ( 5.7 σ ). This is the first direct observation of ν e interactions at a particle collider and includes the highest-energy ν e and ν μ ever detected from an artificial source. The interaction cross section per nucleon σ / E ν is measured over an energy range of 560–1740 GeV (520–1760 GeV) for ν e ( ν μ ) to be ( 1.2 − 0.7 + 0.8 ) × 10 − 38     cm 2   GeV − 1 [ ( 0.5 ± 0.2 ) × 10 − 38     cm 2   GeV − 1 ], consistent with standard model predictions. These are the first measurements of neutrino interaction cross sections in those energy ranges. Published by the American Physical Society 2024