Measurement of the flux and zenith-angle distribution of upward through-going muons by Super-Kamiokande

TL;DR

This study measures the flux and angular distribution of upward muons in Super-Kamiokande, finding results consistent with neutrino oscillations but not with no-oscillation predictions.

Contribution

It provides the first detailed flux and angular distribution measurements of upward muons, supporting neutrino oscillation hypotheses.

Findings

Measured muon flux agrees with predictions within errors.

Observed zenith angle distribution deviates from no-oscillation models.

Results support neutrino oscillation parameters with  > 0.4 and  between 10^{-3} and 10^{-1} eV^2.

Abstract

A total of 614 upward through-going muons of minimum energy 1.6 GeV are observed by Super-Kamiokande during 537 detector live days. The measured muon flux is 1.74+/-0.07(stat.)+/-0.02(sys.)x10^{-13}cm^{-2}s^{-1}sr^{-1} compared to an expected flux of 1.97+/-0.44(theo.)x10^{-13}cm^{-2}s^{-1}sr^{-1}. The absolute measured flux is in agreement with the prediction within the errors. However, the zenith angle dependence of the observed upward through-going muon flux does not agree with no-oscillation predictions. The observed distortion in shape is consistent with the \nu_\mu <-> \nu_\tau oscillation hypothesis with \sin^22\theta > 0.4 and 1x10^{-3} < \Delta m^2 < 1x10^{-1} eV^{2} at 90% confidence level.