Search for nonstandard neutrino interactions with IceCube DeepCore

As atmospheric neutrinos propagate through the Earth, vacuumlike oscillations are modified by Standard Model neutral- and charged-current interactions with electrons. Theories beyond the Standard Model introduce heavy, TeV-scale bosons that can produce nonstandard neutrino interactions. These additional interactions may modify the Standard Model matter effect producing a measurable deviation from the prediction for atmospheric neutrino oscillations. The result described in this paper constrains nonstandard interaction parameters, building upon a previous analysis of atmospheric muon-neutrino disappearance with three years of IceCube DeepCore data. The best fit for the muon to tau flavor changing term is ${\epsilon }_{\mu \tau }=-0.0005$, with a 90% C.L. allowed range of $-0.0067<{\epsilon }_{\mu \tau }<0.0081$. This result is more restrictive than recent limits from other experiments for ${\epsilon }_{\mu \tau }$. Furthermore, our result is complementary to a recent constraint on ${\epsilon }_{\mu \tau }$ using another publicly available IceCube high-energy event selection. Together, they constitute the world’s best limits on nonstandard interactions in the $\mu -\tau$ sector.

Figure 1

Muon neutrino (top) and antineutrino (bottom) survival probability at zenith angle $\cos \theta =-1$, corresponding to vertically up going neutrinos that traverse the entire diameter of the Earth, for global best-fit oscillations (solid) and ${\epsilon }_{\mu \tau }=0.01$ NSI, close to the current Super-Kamiokande limits (dashed)[26]. NSI effects are visible in the full neutrino energy range of 10–1000 GeV.

Figure 2

Detector geometry: green circles represent IceCube strings and red ones DeepCore strings.

Figure 3

Expected pulls of predicted event numbers as a function of neutrino energy and zenith angle. The left (right) panel compares ${\epsilon }_{\mu \tau }=-0.01$ (${\epsilon }_{\mu \tau }=0.01$) to the standard neutrino oscillation matter effects (SI) expectation.

Figure 4

Data (black points) and Monte Carlo (solid lines) comparisons for the best-fit nuisance parameters of this analysis, as a function of the arrival direction, $\cos ({\theta }_z^{\mathrm{reco}})$, in the eight different energy bins. The orange color corresponds to the best-fit point (${\epsilon }_{\mu \tau }=-5\times {10}^{-4}$) and the light green to ${\epsilon }_{\mu \tau }=0.015$. The error bars include statistical uncertainties only.

Figure 5

Confidence limits from this analysis on the NSI parameter ${\epsilon }_{\mu \tau }$ using the event selection from [14, 54] shown as solid vertical red lines. Similarly, dashed vertical red lines show the 90% credibility interval using a flat prior on ${\epsilon }_{\mu \tau }$ and where we have profiled over the nuisance parameters. The light blue vertical lines show the Super-Kamiokande 90% C.L. [26]. The light green lines show the 90% credibility region from [24]. Finally, the horizontal dash-dot line indicates the value of $-2\mathrm{\Delta }\mathrm{LLH}$ that corresponds to a 90% confidence interval according to Wilks’s theorem.

Figure 6

Correlation matrix of the nuisance and physics parameters considered in this analysis calculated at the maximum likelihood solution. The color scale shows the correlation coefficient ($\rho$).