A Measurement of Atmospheric Neutrino Oscillation Parameters by Super-Kamiokande I

TL;DR

Super-Kamiokande analyzes atmospheric neutrinos using 1489 live-days of SK-I data, spanning $E_\nu$ from 100 MeV to 10 TeV, to test two-flavor $\nu_\mu \leftrightarrow \nu_\tau$ oscillations. A global $\chi^2$ fit incorporates fully-contained, partially-contained, and upward-going muon samples across 180 bins with 39 systematic nuisance parameters, yielding a best-fit $\sin^22\theta = 1.00$ and $\Delta m^2 = 2.1\times10^{-3}\ \mathrm{eV}^2$, with a 90% C.L. region of $1.5\times10^{-3} < \Delta m^2 < 3.4\times10^{-3}\ \mathrm{eV}^2$ and $\sin^22\theta > 0.92$. No-oscillation is strongly disfavored, and results are consistent with complementary analyses (e.g., L/E studies and K2K). The measurement provides one of the most precise determinations of the mixing angle and a robust constraint on the atmospheric mass-squared difference, reinforcing the $\nu_\mu \rightarrow \nu_\tau$ interpretation of atmospheric neutrino oscillations and guiding future long-baseline experiments.

Abstract

We present a combined analysis of fully-contained, partially-contained and upward-going muon atmospheric neutrino data from a 1489 day exposure of the Super--Kamiokande detector. The data samples span roughly five decades in neutrino energy, from 100 MeV to 10 TeV. A detailed Monte Carlo comparison is described and presented. The data is fit to the Monte Carlo expectation, and is found to be consistent with neutrino oscillations of $ν_μ\leftrightarrow ν_τ$ with $\sin^22θ> 0.92$ and $1.5\times 10^{-3} < Δm^2 < 3.4\times 10^{-3}{\rm eV}^2$ at 90% confidence level.

Figures (42)

• Figure 1: The parent neutrino energy distributions for the fully-contained, partially-contained, upward stopping-muon and upward through-going muons samples. Rates for the fully-contained and partially-contained samples are for interactions in the 22.5 kiloton fiducial volume. Taken together, the samples span five decades in neutrino energy.
• Figure 2: (a) The direction averaged atmospheric neutrino energy spectrum for $\nu_{\mu}+\overline{\nu}_{\mu}$ calculated by several authors are shown by solid line Honda:2004yz, dashed line Barr:2004br and dotted line Battistoni:2003ju. (b) The ratio of the calculated neutrino flux. The fluxes calculated in Barr:2004br (solid line) and Battistoni:2003ju (dashed line) are normalized by the flux in Honda:2004yz.
• Figure 3: The flux ratio of $\nu_{\mu} + \overline{\nu}_{\mu}$ to $\nu_e + \overline{\nu}_e$ averaged over all zenith and azimuth angles versus neutrino energy. Solid, dashed and dotted lines show the prediction by Honda:2004yz, Barr:2004br and Battistoni:2003ju, respectively.
• Figure 4: The flux ratios of $\nu_{\mu}$ to $\overline{\nu}_{\mu}$ and $\nu_e$ to $\overline{\nu}_e$ versus neutrino energy. Solid, dashed and dotted lines show the prediction by Honda:2004yz, Barr:2004br and Battistoni:2003ju, respectively (same key as Fig. \ref{['fig:flavor_vs_enu']}).
• Figure 5: The flux of atmospheric neutrinos versus zenith angle. Solid, dashed and dotted lines show the prediction by Honda:2004yz, Barr:2004br and Battistoni:2003ju, respectively (same key as Fig. \ref{['fig:flavor_vs_enu']}).