Measurement of the muon flux at SND@LHC

The SND@LHC experiment investigates neutrinos in the 7.2<η<8.4 forward pseudorapidity range. The detector consists of a veto system, a scintillating fiber tracker interleaved with emulsion cloud chambers, and a downstream muon system. Muons originating from collisions at ATLAS (IP1) constitute the primary background for CC neutrino interactions and determine the replacement frequency of the emulsion target. A precise characterization of this flux is therefore essential. In this work, we report the muon flux measured in the central 31×31cm2 fiducial area of the detector using data from 2023 through 2025. The measured fluxes for proton collisions are: (1.90±0.04)×10-2 nb/cm2 (2023), (3.76 ± 0.09) ×10-2 nb/cm2 (2024), and (2.48 ± 0.05) ×10-2 nb/cm2 (2025). A 2024 reference proton run at s=5.36TeV yielded (4.21 ± 0.14) ×10-2 nb/cm2, providing a direct baseline for the heavy-ion energy regime. The measured fluxes for heavy-ion collisions are (3.11±0.12)×104 nb/cm2, (5.53±0.22)×104 nb/cm2, and (3.24±0.13)×104nb/cm2 in 2023, 2024, and 2025, respectively. Uncertainties are dominated by systematic effects, with the statistical component contributing ≲0.1% to the total uncertainty. These results are in agreement with Monte Carlo predictions.