Strong Constraints on Neutrino Nonstandard Interactions from TeV-Scale ${\nu }_{\mu }$ Disappearance at IceCube

We report a search for nonstandard neutrino interactions (NSI) using eight years of TeV-scale atmospheric muon neutrino data from the IceCube Neutrino Observatory. By reconstructing incident energies and zenith angles for atmospheric neutrino events, this analysis presents unified confidence intervals for the NSI parameter ${\epsilon }_{\mu \tau }$. The best-fit value is consistent with no NSI at a $p$ value of 25.2%. With a 90% confidence interval of $-0.0041\le {\epsilon }_{\mu \tau }\le 0.0031$ along the real axis and similar strength in the complex plane, this result is the strongest constraint on any NSI parameter from any oscillation channel to date.

Figure 1

Muon neutrino oscillogram—an example of how NSI modify predicted neutrino fluxes. Shown here is the probability ratio of NSI-modified oscillations to the SM prediction for atmospheric neutrinos [chosen value is $\mathrm{Re}({\epsilon }_{\mu \tau })=0.0031$, $\mathrm{Im}({\epsilon }_{\mu \tau })=0.0$, the 90% CL bound on positive Re(${\epsilon }_{\mu \tau }$)]. Effects include flux disappearance at energies of 1 TeV and above for events crossing the largest Earth baselines [$\cos (\theta )=-1$] and flux enhancement at $\sim 100\mathrm{GeV}$. Note that the neutrino true energy range corresponds to the stated muon proxy energy range, and that the maximum disappearance for this value of ${\epsilon }_{\mu \tau }$ is $\sim 3.4\%$.

Figure 2

Real-only result. Top: the $-2\mathrm{\Delta }LLH$ profile from the fit to data. Blue-shaded regions correspond to the CL regions determined from the $-2\mathrm{\Delta }LLH$ values. Bottom: comparison of the 90% CL limits from this analysis to IceCube’s previous real-only ${\epsilon }_{\mu \tau }$ search [38] and the Super-Kamiokande experiment’s inaugural constraints [48].

Figure 3

Complex result. Confidence level regions for complex ${\epsilon }_{\mu \tau }$ in blue-shaded regions, with the analysis 90% CL sensitivity in green and the red cross marking the data’s best fit.

Figure 4

Global comparison. Comparison of the analysis 90% CL sensitivity and result to the DeepCore 3-year, 5.6–100 GeV result [36]. Green and yellow regions represent 90% CL sensitivity envelopes of symmetrically counted 68 and 95% (respectively) regions calculated from 1000 pseudoexperiment trials.