Evidence for oscillation of atmospheric neutrinos

TL;DR

This paper provides evidence for atmospheric neutrino oscillations, showing a zenith angle dependent muon neutrino deficit inconsistent with flux predictions, supporting the nu_mu <-> nu_tau oscillation hypothesis.

Contribution

First experimental evidence of atmospheric neutrino oscillations with specific oscillation parameters from Super-Kamiokande data.

Findings

Muon neutrino deficit varies with zenith angle.

Data supports nu_mu <-> nu_tau oscillations.

Oscillation parameters constrained to sin^2(2θ)>0.82, 5x10^-4 < Δm^2 < 6x10^-3 eV^2.

Abstract

We present an analysis of atmospheric neutrino data from a 33.0 kiloton-year (535-day) exposure of the Super-Kamiokande detector. The data exhibit a zenith angle dependent deficit of muon neutrinos which is inconsistent with expectations based on calculations of the atmospheric neutrino flux. Experimental biases and uncertainties in the prediction of neutrino fluxes and cross sections are unable to explain our observation. The data are consistent, however, with two-flavor nu_mu <-> nu_tau oscillations with sin^2(2theta)>0.82 and 5x10^-4 < delta m^2 < 6x10^-3 eV^2 at 90% confidence level.