Speaker
Description
The dominant background at the SND@LHC experiment consists of muons reaching the detector after traversing several tens of meters of rock. Monte Carlo simulations were instrumental in the experiment design and the background study. For the latter, a two-step workflow was adopted, first simulating with FLUKA proton$-$proton collisions in ATLAS and recording secondary muons on a virtual interface plane in the rock, and then propagating them to SND@LHC with Geant4. Benchmarking of simulated integral fluxes against Run-3 measurements showed a level of agreement within 10$-$30$\%$ and enabled the interpretation of the significant variations that were observed as a function of the LHC optics and beam crossing plane. In particular, the role of diffractive proton losses in an accelerator cell upstream of the detector was highlighted. On this basis, effective mitigation strategies, such as orbit bumps displacing these losses to other cells, were explored. For the HL-LHC configuration of Run-4, first estimates indicate a significantly higher muon background than in Run-3, reflecting not only the planned luminosity increase but also the larger leakage due to the magnet aperture enlargement.
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