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

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We present the results of the charge ratio ( R ) and polarization ( P0μ ) measurements using decay electron events collected between September 2008 and June 2022 with the Super-Kamiokande detector. Because of its underground location and long operation, we are able to perform high-precision measurements by accumulating cosmic-ray muons. We measured the muon charge ratio to be R=1.32±0.02(stat+syst) at EμcosθZenith=0.7−0.2+0.3 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 indicating a tension with the πK model of 1.9σ . We also measured the muon polarization at the production location to be P0μ=0.52±0.02 (stat+syst) at the muon momentum of 0.9−0.1+0.6 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 atmospheric neutrino simulations. Published by the American Physical Society 2024

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