Neutrino-induced upward stopping muons in Super-Kamiokande

A total of 137 upward stopping muons of minimum energy 1.6 GeV are observed by Super-Kamiokande during 516 detector live days. The measured muon flux is 0.39 +/- 0.04(stat.) +/- 0.02(syst.) X 10(-13) cm(-2)s(-1)sr(-1) compared to an expected flux of 0.73 +/- 0.16(theo.)X 10(-13) cm(-2)s(-1)sr(-1). Using our previously-published measurement of the upward through-going muon flux, we calculate the stopping/through-going flux ratio R, which has less theoretical uncertainty. The measured value of R = 0.22 +/- 0.02(stat.) +/- 0.01(syst.) is significantly smaller than the value 0.37(-0.04)(+0.05)(theo.) expected using the best theoretical information (the probability that the measured R is a statistical fluctuation below the expected value is 0.39%). A simultaneous fitting to zenith angle distributions of upward stopping and through-going muons gives a result which is consistent with the hypothesis of neutrino oscillations with the parameters sin(2)2 theta > 0.7 and 1.5 X 10(-3) < Delta m(2) < 1.5 X 10(-2) eV(2) at 90% confidence level, providing a confirmation of the observation of neutrino oscillations by Super-Kamiokande using the contained atmospheric neutrino events. (C) 1999 Published by Elsevier Science B.V. All rights reserved.