As cosmic rays collide with particles in the Earth’s atmosphere, air showers containing atmospheric muons and neutrinos are produced. The atmospheric neutrinos are then detected by DeepCore, a denser and smaller array of sensors in the center of the IceCube Neutrino Observatory at the South Pole. Compared to the main IceCube detector, DeepCore is sensitive to neutrinos down to energies of only a few GeV, or a 100 times lower in energy.
On their way to IceCube, atmospheric neutrinos travel long distances during which they morph into different types or “flavors”—electron, muon, and tau—in a phenomenon called neutrino oscillation. These oscillations occur as a result of the “mixing” between neutrino mass and different flavor states, but the detection of atmospheric neutrino oscillations can be difficult.
The IceCube Upgrade, set to be installed in a few months, will add seven more closely spaced and densely instrumented strings of optical sensors in the central part of the array, which will greatly enhance IceCube’s sensitivity to low energies and, thus, significantly improve measurements of atmospheric neutrino oscillations. The IceCube Collaboration presents a new prediction of the expected performance of the IceCube Upgrade for several physics analyses using atmospheric neutrino oscillations. These results, submitted to Physical Review D, are the first sensitivity studies to combine data from the IceCube Upgrade with 12 years of existing DeepCore data.
“The last estimation of the IceCube Upgrade’s sensitivities to atmospheric neutrino oscillations was more than five years ago,” says Jan Weldert, a postdoctoral researcher at the University of Mainz and one of the main analyzers of the study. “Now that the IceCube Upgrade is ready to be installed, we wanted to update these projections and demonstrate its physics potential at GeV energies.”
Kayla DeHolton, a postdoctoral researcher at Penn State, and Rasmus Ørsøe, a postdoctoral associate at Technische Universität München, were also main analyzers of the study.
“One of the major changes for the IceCube Upgrade is that the modules each contain multiple photosensors (PMTs), whereas in the current detector, each module contains only one photosensor,” explains DeHolton. “Therefore, to fully utilize the new information we will receive, many new tools were designed to take these multi-PMT modules into account.”
For the study, the researchers improved the software, developed a new simulation, and designed new data cleaning and reconstruction tools specifically for the IceCube Upgrade and the new multi-PMT modules.
“Ultimately, our new cleaning method represents a significant improvement over existing approaches and can be reused beyond the scope of the IceCube Upgrade—in other neutrino telescopes with multi-PMT optical modules or in those with high noise rates,” says Ørsøe. “Both our cleaning and reconstruction algorithms are open-source.”
Combining three years of IceCube Upgrade data and 12 years of DeepCore data, they expect IceCube to have a competitive measurement of atmospheric neutrino oscillation parameters, world-leading precision for measuring tau neutrino appearance, and enhanced sensitivity for determining the neutrino mass ordering.
+ info “Physics potential of the IceCube Upgrade for atmospheric neutrino oscillations,” IceCube Collaboration: R. Abbasi et al. Submitted to Physical Review D. arxiv.org/abs/2509.13066
