IceCube, highly successful and the only cubic-kilometer neutrino detector constructed to date, uses natural ice as a Cherenkov medium. IceCube not only proved it was possible to build such a large scientific facility at the South Pole, the lessons learned from its operation have resulted in an even more optimized and efficient design for the next-generation detector.
Science has followed the detector’s performance. IceCube’s discovery of astrophysical neutrinos revealed the potential to explore our universe with high-energy neutrinos, at the PeV scale and above, where most of the universe is opaque to high-energy photons. More recently, a multimessenger campaign following up on an IceCube high-energy neutrino alert led to the first evidence for a likely source of extragalactic neutrinos and of high-energy cosmic rays, the distant blazar TXS0506+056.
An in-depth exploration of the neutrino universe requires a next-generation IceCube detector. Named IceCube-Gen2 and based on the robust design of the current detector, the goal for the new observatory is to deliver statistically significant samples of very high energy astrophysical neutrinos, in the PeV to EeV range, and yield hundreds of neutrinos across all flavors at energies above 100 TeV. This will enable detailed spectral studies, significant point source detections, and new discoveries. While plans for this large-scale upgrade are under development, investigators have secured funding for mid-scale instrumentation advancements that will produce science results nearly a decade earlier than the full facility expansion.
This initiative will deploy 750 advanced photodetectors and calibration devices inside the existing IceCube detector. The new instrumentation will improve our understanding of how the light emitted by neutrino interactions in the ice travels throughout the detector, effectively bringing the neutrinos into sharper focus. The IceCube Upgrade will thus allow us to increase the sensitivity of the present telescope. The sharper resolution achieved through the upgrade can be retroactively applied to data already acquired and stored during the first decade of IceCube’s operation, immediately providing a major improvement in IceCube’s sensitivity.
IceCube instruments a cubic kilometer of clear Antarctic ice with 86 strings of sensors at depths between 1450 and 2450 meters. The observatory includes a densely instrumented subdetector, DeepCore, and a surface air shower array, IceTop. The IceCube Upgrade will deploy seven new strings inside the current array.
In addition, new sensors will provide a unique opportunity to measure the properties of neutrinos, the least understood of the fundamental particles discovered to date. Cosmic ray interactions in Earth’s atmosphere provide a copious natural source of neutrinos. As neutrinos travel through space, they change from one type to another—a purely quantum-mechanical process known as neutrino oscillation. The IceCube Upgrade will provide the first precision measurement of the number of tau neutrinos appearing as a result of these oscillations. A measurement inconsistent with the poorly constrained current theory would be a smoking gun pointing to undiscovered types of neutrinos or to new physics.
IceCube-Gen2, a ten-cubic-kilometer detector
The incredible clarity of the Antarctic glacier, revealed by the construction and operation of IceCube, will allow the spacing between light sensors to exceed 250 meters, instead of the current 125 meters in IceCube. The deployment of sensors on strings with larger spacings will enable the IceCube-Gen2 instrumented volume to rapidly grow at modest costs.
A possible IceCube-Gen2 configuration. IceCube, in red, and the infill subdetector DeepCore, in green, show the current configuration. The blue volume shows the full instrumented next-generation detector.
IceCube-Gen2 will benefit from the successful designs of the hot water drill systems and the digital optical modules in the original IceCube project. Minimal modifications will target improvements focused on modernization, efficiency, and cost savings. Because of its digital architecture, the next-generation facility can be operated without a significant increase in costs.
By roughly doubling the instrumentation already deployed, the telescope will achieve a tenfold increase in volume to about 10 cubic kilometers, aiming at an order of magnitude increase in neutrino detection rates. IceCube-Gen2 will provide an unprecedented view of the high-energy universe, taking neutrino astronomy to new levels of discovery.
Neutrino astronomy will be only one topic in the rich science program of a next-generation neutrino observatory. Besides studying the properties of cosmic rays and searching for signatures of neutrino physics beyond the Standard Model, this world-class, multipurpose detector will remain a discovery instrument for unanticipated physics and astrophysics. The observation of a supernova in our galactic neighborhood in coincidence with astronomical and gravitational wave instruments would be the astronomical event of the century.
See the IceCube Upgrade press release.
Read Neutrino astronomy with the next-generation IceCube Neutrino Observatory on arXiv.