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) compare
d to an expected flux of 0.73 +/- 0.16(theo.)X 10(-13) cm(-2)s(-1)sr(-1). U
sing 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)(the
o.) expected using the best theoretical information (the probability that t
he 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 hypoth
esis 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, prov
iding a confirmation of the observation of neutrino oscillations by Super-K
amiokande using the contained atmospheric neutrino events. (C) 1999 Publish
ed by Elsevier Science B.V. All rights reserved.