Measurements of the charge ratio and polarization of cosmic-ray muons with the Super-Kamiokande detector

We present the results of the charge ratio (R) and polarization (Pμ₀) measurements using the decay electron events collected from 2008 September to 2022 June by the Super-Kamiokande detector. Because of its underground location and long operation, we performed high precision measurements by accumulating cosmic-ray muons. We measured the muon charge ratio to be R=1.32 ± 0.02 (stat.+syst.) at Eμcos θZenith=0.7+0.3-0.2 TeV, where Eμ is the muon energy and θZenith is the zenith angle of incoming cosmic-ray muons. This result is consistent with the Honda flux model while this suggests a tension with the π K model of 1.9σ. We also measured the muon polarization at the production location to be Pμ₀=0.52 ± 0.02 (stat.+syst.) at the muon momentum of 0.9+0.6-0.1 TeV/c at the surface of the mountain; this also suggests a tension with the Honda flux model of 1.5σ. This is the most precise measurement ever to experimentally determine the cosmic-ray muon polarization near 1~TeV/c. These measurement results are useful to improve the atmospheric neutrino simulations.