Latest results from the IceCube Neutrino Observatory

Abstract: The IceCube Neutrino Observatory has opened a new window into the high-energy Universe, providing measurements of neutrinos over a broad energy range. This contribution presents recent results, including a follow-up on the first identification of a steady neutrino source NGC 1068, measurements of the flavor composition of the diffuse astrophysical flux, limits on prompt atmospheric neutrinos, and searches for neutrinos from dark matter annihilation in the Sun. These measurements probe neutrino production mechanisms, fundamental particle interactions, and physics beyond the Standard Model. Looking forward, the recently deployed IceCube Upgrade will enhance sensitivity to lower-energy neutrinos and reduce systematic uncertainties, while the planned IceCube-Gen2 will expand the detector volume, increase the neutrino detection rate, and extend energy reach, enabling more detailed studies of cosmic sources and high-energy particle physics.

• The paper validates steady neutrino emission from X-ray-bright AGNs with >5σ significance over 13.1 years of data.
• The paper employs track and cascade event reconstruction to measure neutrino flavor composition consistent with pion decay, constraining exotic physics.
• The paper sets new limits on prompt atmospheric neutrinos and spin-dependent dark matter interactions, paving the way for future IceCube upgrades.

IceCube Neutrino Observatory: Recent High-Energy Neutrino Astrophysics and Particle Physics Results

Detector Overview and Methodological Advancements

The IceCube Neutrino Observatory, a cubic-kilometer Cherenkov array situated beneath the Antarctic ice, leverages 5160 optical modules on 86 strings to observe neutrino interactions spanning the $\sim 10$ GeV to multi-PeV regime. Track and cascade event reconstruction are enabled by the spatial-temporal resolution of photon signals. DeepCore, the denser sub-array, is optimized for $\mathcal{O}(10)$ GeV atmospheric neutrino oscillation studies, facilitating a robust background model crucial for high-confidence astrophysical event selection. The detector architecture permits cross-section measurements at energies beyond terrestrial accelerator capabilities and establishes the foundation for multi-flavor analysis.

Steady Astrophysical Neutrino Emission from X-ray-Bright AGNs

IceCube has confirmed NGC 1068 as the first statistically significant ($>5\sigma$) steady extragalactic neutrino source, characterized by an unbroken power law with spectral index $\gamma = 3.4 \pm 0.2$ absent corresponding gamma-ray emission. A targeted analysis over 13.1 years has extended the source list to X-ray-bright AGNs, revealing a $3.3\sigma$ excess from an ensemble population consistent with neutrino production in the AGN corona. The X-ray photons serve as targets for photomeson interactions with $\sim 100$ TeV protons, supporting models of neutrino emission from dense environments near supermassive black holes. These results contrast with gamma-ray-bright AGNs, suggesting unique astrophysical accelerators and particle interactions.

Figure 1: All-flavor neutrino flux measurements for the top 4 X-ray-bright AGNs, including the NGC 1068 excess, contextualized by the diffuse flux measurement.

Astrophysical Neutrino Flavor Composition

The flavor composition of the diffuse astrophysical flux constitutes a direct diagnostic of production channels and propagation effects. Using an internally contained vertex sample with $\sim11$ years of data, IceCube achieves sensitivity to all flavors via topology classification (tracks, cascades, double cascades). The measured ratios $f_e:f_{\mu}:f_{\tau} = 0.30:0.37:0.33$ align closely with standard oscillation predictions assuming pion decay origins, ruling out extreme neutron decay scenarios with $>$99\% confidence. No significant evidence for non-standard flavor transformation or exotic physics has been observed at current statistics.

Figure 2: Measured flavor composition at Earth versus theoretical benchmarks for different production mechanisms, demonstrating consistency with pion decay and oscillation.

Constraints on Prompt Atmospheric Neutrinos

Prompt atmospheric neutrinos, originating from decay of charmed mesons produced in cosmic ray air showers, remain a critical background in astrophysical flux interpretation and offer insight into high-energy hadronic interaction regimes inaccessible at accelerators. IceCube’s combined cascade and track analysis imposes a stringent upper limit: $$\Phi_\text{prompt} < 4\times10^{-16}~\text{GeV}^{-1}~\text{s}^{-1}~\text{m}^{-2}~\text{sr}^{-1}$$ at 10 TeV, with observed events consistent with zero. This result constrains charm production models in atmospheric showers and supports the robustness of astrophysical flux extraction.

Figure 3: IceCube upper limit on prompt neutrino flux, juxtaposed with model predictions and SPL fits for the astrophysical component.

Indirect Dark Matter Searches in the Sun

IceCube has advanced the world-leading constraints on spin-dependent WIMP-proton cross sections via searches for energetic neutrinos from the solar core. DeepCore and IceCube datasets spanning over a decade yield no excess above the background, with limits superior to direct detection methodologies for masses $\mathcal{O}(10)$0 GeV. Capture-annihilation equilibrium assumptions enhance sensitivity, enabling robust exclusion regions in the parameter space of dark matter models.

Figure 4: Upper limits on spin-dependent dark matter-proton scattering from IceCube, contrasted with direct and indirect detection bounds.

Future Trajectory: IceCube Upgrade and Gen2

The IceCube Upgrade, with densely instrumented strings and advanced calibration, will provide improved statistical and systematic precision for low-energy event analyses, including oscillation parameter measurements and refined dark matter searches. The planned IceCube-Gen2 expansion multiplies instrumented volume by a factor of eight, increases cosmic neutrino detection rates by an order of magnitude, and extends sensitivity to EeV energies. Integration of radio and surface arrays will facilitate multimessenger studies and expand theoretical reach in high-energy particle astrophysics.

Conclusion

Recent IceCube results have validated the existence of steady neutrino emission from X-ray-bright AGNs, provided precise flavor composition measurements consistent with standard oscillation paradigms, set stringent limits on prompt atmospheric neutrinos, and delivered world-leading constraints on solar dark matter-induced neutrinos. The ongoing detector upgrades and expansion projects position IceCube to further elucidate the mechanisms of cosmic particle acceleration, fundamental neutrino interactions, and potential new physics, catalyzing future advances in astroparticle and particle physics.