FASER Collab.
First Measurement of the νe and νμ Interaction Cross Sections at the LHC with FASER's Emulsion Detector
This paper presents the first results of the study of high-energy electron and muon neutrino charged-current interactions in the FASERν emulsion/tungsten detector of the FASER experiment at the LHC. A subset of the FASERν volume, which corresponds to a target mass of 128.6 kg, was exposed to neutrinos from the LHC pp collisions with a centre-of-mass energy of 13.6 TeV and an integrated luminosity of 9.5 fb−1. Applying stringent selections requiring electrons with reconstructed energy above 200 GeV, four electron neutrino interaction candidate events are observed with an expected background of 0.025+0.015−0.010, leading to a statistical significance of 5.2σ. This is the first direct observation of electron neutrino interactions at a particle collider. Eight muon neutrino interaction candidate events are also detected, with an expected background of 0.22+0.09−0.07, leading to a statistical significance of 5.7σ. The signal events include neutrinos with energies in the TeV range, the highest-energy electron and muon neutrinos ever detected from an artificial source. The energy-independent part of the interaction cross section per nucleon is measured over an energy range of 560-1740 GeV (520-1760 GeV) for νe (νμ) to be (1.2+0.8−0.7)×10−38 cm2GeV−1 ((0.5±0.2)×10−38 cm2GeV−1), consistent with Standard Model predictions. These are the first measurements of neutrino interaction cross sections in those energy ranges.