Measurement of the muon flux at SND@LHC

The SND@LHC experiment investigates neutrinos in the 7.2< η < 8.4 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 × 31 31 × 31 cm² cm 2 fiducial area of the detector using data from 2023 through 2025. The measured fluxes for proton collisions are: (1.90±0.04) × 10⁻² × 10 - 2 nb/cm² nb/cm 2 (2023), (3.76 ± 0.09) × × 10⁻² 10 - 2 nb/cm² nb/cm 2 (2024), and (2.48 ± 0.05) × 10⁻² × 10 - 2 nb/cm² nb/cm 2 (2025). A 2024 reference proton run at √s = 5.36 TeV s = 5.36 TeV yielded (4.21 ± 0.14) × × 10⁻² 10 - 2 nb/cm² nb/cm 2 , providing a direct baseline for the heavy-ion energy regime. The measured fluxes for heavy-ion collisions are (3.11±0.12) × 10⁴