Measurement of the flux and zenith-angle distribution of upward through-going muons in Kamiokande II+III

TL;DR

This paper reports the measurement of upward through-going muon flux and zenith-angle distribution in Kamiokande II+III, providing evidence consistent with neutrino oscillations through observed angular dependence.

Contribution

First precise measurement of muon flux and angular distribution in Kamiokande II+III supporting neutrino oscillation evidence.

Findings

Measured muon flux agrees with theoretical predictions within errors.

Observed zenith-angle distribution supports neutrino oscillation hypothesis.

Data consistent with previous atmospheric neutrino studies.

Abstract

The flux of upward through-going muons of minimum (mean) threshold energy > 1.6 (3.0) GeV is measured, based on a total of 372 events observed by the Kamiokande II+III detector during 2456 detector live days. The observed muon flux was (1.94+-0.10(stat.)+0.07-0.06(sys.))*10^-13 /cm^2/s/sr, which is compared to an expected value of (2.46+-0.54(theo.))*10^-13/cm^2/s/sr. The observation is in agreement with the prediction within the errors. The zenith angle dependence of the observed upward through-going muons supports the previous indication of neutrino oscillations made by Kamiokande using sub- and multi-GeV atmospheric neutrino events.