IceCube DeepCore's sensitivity to Non-Standard neutrino Interactions in the Earth

Neutrino oscillations continue to provide one of the most promising avenues for uncovering physics beyond the Standard Model. In particular, beyond-standard-model neutrino matter interactions may perturb neutrino oscillations in matter, leading to an observable signal in long baseline oscillation experiments. Moreover, such interactions can be a possible explanation of the rising tension between T2K and NOvA’s $δ_{\text{CP}}$ measurements. We examine IceCube DeepCore’s sensitivity to these Non-Standard Interactions (NSI) by employing a model-independent NSI parameterization, and examine IceCube DeepCore’s ability to comment on NSI being the cause of the T2K-NOvA $δ_{\text{CP}}$ tension.

💡 Research Summary

This paper evaluates the sensitivity of the IceCube DeepCore detector to non‑standard neutrino interactions (NSI) using 9.28 years of atmospheric neutrino data. The authors adopt a model‑independent NSI framework in which the matter Hamiltonian is perturbed by eight independent parameters (two real diagonal and three complex off‑diagonal εαβ). By removing an unphysical global phase and setting ε′ = 0, δNS = 0, and α₁ = α₂ = 0 (since DeepCore has limited CP‑phase sensitivity), the parameter space collapses to three physically relevant quantities: an overall scaling ε and two rotation angles φ₁₂ and φ₁₃ that control first‑order NSI effects in the e–μ and e–τ sectors, respectively. This reduced description is termed the Generalized Matter Potential (GMP). In the Standard Interactions (SI) limit, ε = 1 and φ₁₂ = φ₁₃ = 0.

The analysis uses a reconstruction algorithm based on convolutional neural networks to classify events into tracks (μ‑charged‑current), cascades (e, τ‑charged‑current and neutral‑current), and mixed topologies. Events are binned in 12 logarithmic energy bins from 5 to 100 GeV and 8 bins of cosine zenith angle (‑1 ≤ cos θ ≤ 0). Compared with the previous three‑year DeepCore NSI study, the dataset is roughly four times larger and systematic uncertainties have been better constrained, leading to a substantial improvement in statistical power.

Sensitivity is quantified with a modified χ² statistic, χ²_mod = (N_obs − N_exp)² / (σ² + N_exp), where the denominator accounts for finite Monte‑Carlo statistics. The SI hypothesis is taken as pseudo‑data, and χ²_mod is computed for each NSI hypothesis. The resulting 1σ intervals for the GMP parameters are:

• ε: (−1.67, −0.39) for the inverted mass ordering and (0.36, 2.64) for the normal ordering,
• φ₁₂: (−4.15°, 4.72°),
• φ₁₃: (−8.7°, 9.28°).

These limits improve by a factor of 2–3 over the earlier three‑year analysis, establishing IceCube DeepCore as the leading experiment for these particular NSI combinations.

The authors also examine the traditional NSI parameters εₑμ and εₑτ, which have been proposed as a possible resolution of the ∼2σ tension between the δ_CP measurements of T2K and NOvA. Using the best‑fit values from the combined T2K‑NOvA analysis (reference