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.) × 10-13 cm-2s-1sr-1 compared to an expected flux of 0.73 ± 0.16(theo.) × 10-13 cm-2s-1sr-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 sin22θ > 0.7 and 1.5 × 10-3 < Δm2 < 1.5 × 10-2 eV2 at 90% confidence level, providing a confirmation of the observation of neutrino oscillations by Super-Kamiokande using the contained atmospheric neutrino events.
|Original language||English (US)|
|Number of pages||9|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - 1999|
Bibliographical noteFunding Information:
We gratefully acknowledge the cooperation of the Kamioka Mining and Smelting Company. The Super-Kamiokande experiment has been built and operated from funding by the Japanese Ministry of Education, Science, Sports and Culture, and the United States Department of Energy.
- Atmospheric muon neutrinos
- Cosmic rays
- Neutrino oscillations
- Upward stopping muons
- Upward throughgoing muons