Multimuon events from cosmic rays in ALICE

ALICE experiment at CERN Large Hadron Collider, located 52 meters underground, carried out a cosmic data-taking campaign in the period 2015–2018 corresponding to 62.5 days of live time. In this work the analysis of these data is limited to multimuon events defined as events with more than four detected muons. In particular the muon multiplicity distribution (MMD) is studied in the low-intermediate multiplicity (4 < 𝑁 𝜇 < 50), corresponding on average to primary energy from 4 PeV up to 60 PeV. For the higher multiplicities, dominated by large fluctuations, the rate of the high muon multiplicity (HMM) events (𝑁 𝜇 > 100) is measured. The results are compared with the Monte Carlo simulations using three of the main hadronic interaction models describing the air shower development in the atmosphere: QGSJET-II-04, EPOS-LHC, and SIBYLL 2.3d. Two extreme compositions of primary cosmic rays were simulated: pure proton, representing the lightest possible composition, and pure iron, representing an extremely heavy composition. Although the models have difficulty in describing precisely the composition trend of cosmic rays, QGSJET-II-04 is the only model that reproduces reasonably well the MMD and the rate of the HMM events assuming a heavy composition for the entire energy range studied.