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Super-Kamiokande atmospheric neutrino results

Toshiyuki Toshito, the Super-Kamiokande collaboration

TL;DR

Using 79 kt·yr of Super-Kamiokande atmospheric data, the analysis finds the μ-neutrino deficit is best explained by $ν_μ\rightarrowν_τ$ oscillations with $Δm^2 \approx 2.5\times10^{-3}$ eV$^2$ and maximal mixing ($\sin^22\theta \approx 1$). The data disfavors pure $ν_μ\rightarrowν_s$ oscillations at 99% C.L., with complementary samples constraining sterile admixtures via matter effects and NC/enriched channels. A search for charged-current $ν_τ$ appearance yields results consistent with $ν_τ$ appearance at ~2$\sigma$, in line with oscillation predictions. Collectively, the results affirm $ν_μ\rightarrowν_τ$ as the primary atmospheric-neutrino oscillation process and place stringent limits on sterile-neutrino scenarios.

Abstract

We present atmospheric neutrino results from a 79 kiloton year (1289 days) exposure of the Super-Kamiokande detector. Our data are well explained by $ν_μ \to ν_τ$ 2-flavor oscillations. We have been attempting to discriminate between the possible oscillating partners of the muon neutrino as being either the tau neutrino or the sterile neutrino. Pure $ν_μ\toν_s$ oscillation is disfavored at 99% C.L.. Moreover, we performed the appearance search for charged current tau neutrino interactions in the upward-going samples. Our data is consistent with $ν_τ$ appearance at roughly the two-sigma level.

Super-Kamiokande atmospheric neutrino results

TL;DR

Using 79 kt·yr of Super-Kamiokande atmospheric data, the analysis finds the μ-neutrino deficit is best explained by oscillations with eV and maximal mixing (). The data disfavors pure oscillations at 99% C.L., with complementary samples constraining sterile admixtures via matter effects and NC/enriched channels. A search for charged-current appearance yields results consistent with appearance at ~2, in line with oscillation predictions. Collectively, the results affirm as the primary atmospheric-neutrino oscillation process and place stringent limits on sterile-neutrino scenarios.

Abstract

We present atmospheric neutrino results from a 79 kiloton year (1289 days) exposure of the Super-Kamiokande detector. Our data are well explained by 2-flavor oscillations. We have been attempting to discriminate between the possible oscillating partners of the muon neutrino as being either the tau neutrino or the sterile neutrino. Pure oscillation is disfavored at 99% C.L.. Moreover, we performed the appearance search for charged current tau neutrino interactions in the upward-going samples. Our data is consistent with appearance at roughly the two-sigma level.

Paper Structure

This paper contains 6 sections, 4 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Event sample
  3. $\nu_\mu\rightarrow\nu_\tau$ oscillation analysis
  4. Study on $\nu_\mu\rightarrow\nu_\tau$ and $\nu_\mu\rightarrow\nu_{sterile}$
  5. Search for charged current $\nu_{\tau}$
  6. Summary

Figures (4)

  • Figure 1: Zenith angle distribution of Super-Kamiokande 1289 days FC, PC and UPMU samples. Dots, solid line and dashed line correspond to data, MC with no oscillation and MC with best fit oscillation parameters, respectively.
  • Figure 2: 68,90 and 99% confidence level allowed regions for $\nu_\mu\rightarrow \nu_\tau$ oscillation obtained by Super-Kamiokande 1289 days result.
  • Figure 3: Zenith angle distributions of left: NC enriched sample, center: high-energy PC sample, right: up-through-going muon sample.
  • Figure 4: Excluded regions for three oscillation modes. The light(dark) gray region is excluded at 90(99)% C.L. by NC enriched sample and high-energy sample analysis. Thin dotted(solid) line indicates the 90(99)% C.L. allowed regions from 1ring-FC sample analysis.