Measurement of a small atmospheric νμ/νe ratio

From an exposure of 25.5 kiloton-years of the Super-Kamiokande detector, 900 muon-like and 983 electron-like single-ring atmospheric neutrino interactions were detected with momentum p(e) > 100 MeV/c, p(mu) > 200 MeV/c, and with visible energy less than 1.33 GeV. Using a detailed Monte Carlo simulation, the ratio (mu/e)(DATA)/(mu/e)(MC) was measured to be 0.61 +/- 0.03(stat.) +/- 0.05(sys.), consistent with previous results from the Kamiokande, IMB and Soudan-2 experiments, and smaller than expected from theoretical models of atmospheric neutrino production. (C) 1998 Published by Elsevier Science B.V. All rights reserved.