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  • Open Access

All-flavor constraints on nonstandard neutrino interactions and generalized matter potential with three years of IceCube DeepCore data

R. Abbasi et al. (IceCube Collaboration)
Phys. Rev. D 104, 072006 – Published 15 October 2021
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  • INTRODUCTION
  • NEUTRINO FLAVOR TRANSITIONS IN EARTH…
  • EVENT SELECTION WITH ICECUBE DEEPCORE
  • ANALYSIS
  • RESULTS
  • CONCLUSION
  • ACKNOWLEDGMENTS
  • APPENDICES
    • References

    Abstract

    We report constraints on nonstandard neutrino interactions (NSI) from the observation of atmospheric neutrinos with IceCube, limiting all individual coupling strengths from a single dataset. Furthermore, IceCube is the first experiment to constrain flavor-violating and nonuniversal couplings simultaneously. Hypothetical NSI are generically expected to arise due to the exchange of a new heavy mediator particle. Neutrinos propagating in matter scatter off fermions in the forward direction with negligible momentum transfer. Hence the study of the matter effect on neutrinos propagating in the Earth is sensitive to NSI independently of the energy scale of new physics. We present constraints on NSI obtained with an all-flavor event sample of atmospheric neutrinos based on three years of IceCube DeepCore data. The analysis uses neutrinos arriving from all directions, with reconstructed energies between 5.6 GeV and 100 GeV. We report constraints on the individual NSI coupling strengths considered singly, allowing for complex phases in the case of flavor-violating couplings. This demonstrates that IceCube is sensitive to the full NSI flavor structure at a level competitive with limits from the global analysis of all other experiments. In addition, we investigate a generalized matter potential, whose overall scale and flavor structure are also constrained.

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    • Received 14 June 2021
    • Accepted 6 August 2021

    DOI:https://doi.org/10.1103/PhysRevD.104.072006

    Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

    Published by the American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Flavor changing neutral currentsNeutrino interactionsNeutrino oscillations
    1. Physical Systems
    Neutrinos
    Particles & Fields

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    Vol. 104, Iss. 7 — 1 October 2021

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    • Figure 1
      Figure 1

      Pμτ oscillation probability of atmospheric neutrinos crossing the Earth at a zenith angle of cos(ϑ)=−0.75 vs the neutrino energy Eν. Shown are different realizations of three NSI parameters, each varied separately. These exhibit the most prominent features and discrepancies from the SM interactions (SI) case, taking into account the different importance of individual channels. In each panel, the SI case is represented by the black line. Blue dashed lines show the probabilities obtained for negative parameter values, while the red dashed lines are for positive values. Darker colors represent larger absolute values of the respective NSI parameter. Top panel: The effective matter potential ε⊕ of the GMP parametrization (cf. Sec. 2b) with −5≤ε⊕≤5, restricting the matter potential to the ee matrix element, yielding ε⊕=1+εee⊕−εμμ⊕. Apart from the SI case (ε⊕=1), the no interactions case (vacuum, ε⊕=0) is highlighted as a dashed green line. The blue lines denoting negative values are mostly covered by the dark red lines. Center panel: The NSI nonuniversality strength εττ⊕−εμμ⊕, with −0.20≤εττ⊕−εμμ⊕≤0.20. Bottom panel: The NSI coupling strength εμτ⊕, with −0.05≤εμτ⊕≤0.05 and δμτ=0°.

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    • Figure 2
      Figure 2

      Histograms of observed cascadelike events (top row) and tracklike events (bottom row) as a function of cos(ϑreco) for different slices in Ereco (indicated at the top of each panel), together with the MC expectation under the generalized matter potential fit outcome, labeled as “best fit (GMP).” For display purposes, the eight lowest reconstructed energy bins have been merged into four, and only the upgoing region cos(ϑreco)≤0 is shown, where the largest NSI effects are expected. Also shown are the expected event distributions for one particular μ−τ nonuniversality realization (εττ⊕−εμμ⊕=0.10), one μ−τ flavor-violation realization (εμτ⊕=0.050), and one e−μ flavor-violation realization (εeμ⊕=−0.30). In each of these three example NSI scenarios, all nuisance parameters are set to their respective global best fit values within the corresponding NSI parameter space.

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    • Figure 3
      Figure 3

      Observed Δχ2 profiles as a function of the effective NSI flavor nonuniversality parameters εee⊕−εμμ⊕ (left) and εττ⊕−εμμ⊕ (right), together with the central 68.3% and 90% confidence intervals of the experimental sensitivity shown as shaded bands. See text for details.

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    • Figure 4
      Figure 4

      Observed 90% confidence regions in the magnitudes |εαβ⊕| and phases δαβ of the effective flavor-violating NSI coupling strengths εeμ⊕ (left), εeτ⊕ (middle), and εμτ⊕ (right), together with each parameter’s (projected) one-dimensional Δχ2 profile. The best fit point for each pair of parameters is indicated by a cross. The central 68.3% and 90% confidence regions and intervals of the experimental sensitivity are shown as shaded bands. See text for details.

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    • Figure 5
      Figure 5

      Summary of the one-by-one constraints at 90% CL on real NSI nonuniversality and flavor-violation parameters obtained in this study (labeled as “IC DC 2021”) compared to previous limits [30, 31, 64, 65, 70, 71, 72]. Constraints on the magnitudes of complex NSI parameters are given for the respective phase restricted to δαβ=0°, 180°. See text for details.

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    • Figure 6
      Figure 6

      Observed 68.3%, 90%, and 99.7% confidence regions for parameters ε⊕, φ12, and φ13, together with each parameter’s projected one-dimensional Δχ2 profile. The color in each of the three large panels encodes the local value of the projected two-dimensional Δχ2 profile. The best fit point for each pair of parameters is indicated by a cross. The SI/flavor-universal NSI hypothesis, indicated by the dash-dotted lines, is located at ε⊕=1, φ12=0, φ13=0. See text for details. This is the first time the GMP overall scale and flavor structure are constrained simultaneously using IceCube DeepCore data.

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    • Figure 7
      Figure 7

      Oscillation probabilities of atmospheric neutrinos crossing the Earth at zenith angle cos(ϑ)=−0.75 vs the neutrino energy Eν. Shown are different realizations of the effective matter potential strength ε⊕, with −5≤ε⊕≤5. Darker shades represent larger |ε⊕|. The two cases of SI (ε⊕=1, in black) and no interactions (vacuum, ε⊕=0, in green) are highlighted. The the red dashed lines show those obtained for positive parameter values, the blue dashed lines showing the probabilities obtained for negative values are mostly covered by dark red lines. See text for details.

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    • Figure 8
      Figure 8

      Same as Fig. 7, but for different realizations of the NSI nonuniversality strength εττ⊕−εμμ⊕, with −0.20≤εττ⊕−εμμ⊕≤0.20. The blue dashed lines show the probabilities obtained for εττ⊕−εμμ⊕<0, while the red dashed lines show those obtained for εττ⊕−εμμ⊕>0. Darker shades represent larger |εττ⊕−εμμ⊕|. See text for details.

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    • Figure 9
      Figure 9

      Same as Fig. 7, but for different realizations of the NSI coupling strength εμτ⊕, with −0.05≤εμτ⊕≤0.05. The blue dashed lines show the probabilities obtained for εμτ⊕<0, while the red dashed lines show those obtained for εμτ⊕>0. Darker shades represent larger |εμτ⊕|. See text for details.

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    • Figure 10
      Figure 10

      Same as Fig. 7, but for different realizations of the NSI coupling strength εeμ⊕, with −0.30≤εeμ⊕≤0.30. The blue dashed lines show the probabilities obtained for εeμ⊕<0, while the red dashed lines show those obtained for εeμ⊕>0. Darker shades represent larger |εeμ⊕|. See text for details.

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    • Figure 11
      Figure 11

      Same as Fig. 7, but for different realizations of the matter rotation angle φ13, with −20°≤φ13≤20°, keeping ε⊕=0 and φ12=0 fixed. The blue dashed lines show the probabilities obtained for φ13<0, while the red dashed lines show those obtained for φ13>0. Darker shades represent larger |φ13|. See text for details.

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    • Figure 12
      Figure 12

      Statistical pulls on the best fit values for all nuisance parameters to which Gaussian priors are associated (cf. Table 3), shown for each of the fit hypotheses listed in Table 2. More detail can be found in the text.

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