The IceCube Neutrino Observatory at the South Pole searches for high-energy neutrinos that are either produced in the vicinity of distant astrophysical accelerators like black holes and neutron stars (astrophysical neutrinos) or from the interaction of cosmic rays in the Earth’s atmosphere (atmospheric neutrinos).
Atmospheric neutrinos arise primarily from the decay of charged mesons produced in cosmic-ray-induced air showers. There is also the decay of heavy, short-lived mesons containing charm quarks. Although these rarely produced charmed mesons are important sources of atmospheric neutrinos, they decay “promptly” due to their short lifetimes. The measurement of prompt neutrinos promises insights into particle physics beyond terrestrial accelerators and would be an important background to astrophysical neutrino measurements. However, the existence of prompt neutrinos has not been confirmed thus far.
Using a combined dataset, the IceCube Collaboration finds a best-fit prompt contribution above zero, though it still remains consistent with zero within the uncertainties. Their results were presented in a paper submitted to The European Physical Journal C.
For the analysis, the researchers utilized data that contained track- and cascade-like neutrino events. They combined existing data samples of both event selections (a “combined fit”) for a more precise measurement.
“We used a consistent simulation and treatment of systematic uncertainties, which is necessary to harness the full power of the combined dataset,” explains Philipp Fürst, a PhD student at RWTH Aachen University who coled the study with recent PhD graduate Jakob Böttcher. “We ran extensive tests with combinations of diverse flux models, both for the atmospheric and astrophysical flux, to ensure we could produce an unbiased result.”
Prior IceCube searches have resulted in the nonobservation of a prompt neutrino flux and even a preference for an unphysical negative flux.
“Finding the prompt neutrino flux in a diffuse neutrino analysis will remain challenging,” says Böttcher. “Future analyses will require additional data from atmospheric muons to constrain this component.”
+ info “Constraining the Prompt Atmospheric Neutrino Flux Using IceCube’s Cascade and Northern Tracks Samples,” IceCube Collaboration: R. Abbasi et al. Submitted to The European Physical Journal C. arxiv.org/abs/2512.17760