Measurement of the muon flux at the SND@LHC experiment

The Scattering and Neutrino Detector at the LHC (SND@LHC) 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 100 GeV 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 $×$ 18 cm ${}^{2}$ area in the emulsion is: $\begin{array}{c}1.5±0.1\left(\text{stat}\right)×{10}^{4}\phantom{\rule{0.166667em}{0ex}}{\text{fb/cm}}^{2}.\end{array}$ The muon flux per integrated luminosity through a 31 $×$ 31 cm ${}^{2}$ area in the centre of the SciFi is: $\begin{array}{c}2.06±0.01\left(\text{stat}\right)±0.12\left(\text{sys}\right)×{10}^{4}{\text{fb/cm}}^{2}\end{array}$ The muon flux per integrated luminosity through a 52 $×$ 52 cm ${}^{2}$ area in the centre of the downstream muon system is: $\begin{array}{c}2.35±0.01\left(\text{stat}\right)±0.10\left(\text{sys}\right)×{10}^{4}\phantom{\rule{0.166667em}{0ex}}{\text{fb/cm}}^{2}\end{array}$ 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.