Measurement of the muon flux at the SND@LHC experiment

The Scattering and Neutrino Detector at the LHC (\SND) started taking data at the beginning of Run 3 of the LHC. The experiment is designed to perform measurements with neutrinos produced in proton-proton collisions at the LHC in an energy range between 100GeV and 1 TeV. It covers a previously unexplored pseudo-rapidity range of $7.2<\eta<8.4$. The detector is located 480 m downstream of the ATLAS interaction point in the TI18 tunnel. It comprises a veto system, a target consisting of tungsten plates interleaved with nuclear emulsion and scintillating fiber (SciFi) trackers, followed by a muon detector (UpStream, US and DownStream, DS). In this article we report the measurement of the muon flux in three subdetectors: the emulsion, the SciFi trackers and the DownStream Muon detector. The muon flux per integrated luminosity through an 18$\times$18 cm$^{2}$ area in the emulsion is $1.5 \pm 0.1(\textrm{stat}) \times 10^4\,\textrm{fb/cm}^{2}$. The muon flux per integrated luminosity through a 31$\times$31 cm$^{2}$ area in the centre of the SciFi is $2.06\pm0.01(\textrm{stat})\pm0.12(\textrm{sys}) \times 10^{4} \textrm{fb/cm}^{2}$. The muon flux per integrated luminosity through a 52$\times$52 cm$^{2}$ area in the centre of the downstream muon system is $2.35\pm0.01(\textrm{stat})\pm0.10(\textrm{sys}) \times 10^{4}\,\textrm{fb/cm}^{2}$. The total relative uncertainty of the measurements by the electronic detectors is 6 $\%$ for the SciFi and 4 $\%$ for the DS measurement. The Monte Carlo simulation prediction of these fluxes is 20-25 $\%$ lower than the measured values.