IceCube Upgrade: An IceCube Extension for Precision Neutrino Physics and Astrophysics

Embedded deep in the ice cap at the South Pole, the IceCube Neutrino Observatory (ICNO) is the world's unique, largest, and most sensitive high energy neutrino telescope. It is a one-billion-ton detector that uses the deep Antarctic ice as a medium to detect high energy atmospheric and astrophysical neutrinos. Most of the neutrinos observed by IceCube exhibit energies in the range expected for atmospheric neutrinos that originate from decays of elementary particles produced in extensive air showers by cosmic rays coming from nearby sectors of the Milky Way Galaxy. While these can be used to measure the fundamental properties of neutrinos, astrophysical neutrinos at higher energies are key probes of the high-energy phenomena in the Universe. Because of their unique properties, neutrinos pass almost freely through even dense volumes of space and are not deflected by galactic or extra-galactic magnetic fields and traverse the photon-filled universe unhindered. Thus, neutrinos provide direct information about the dynamics and interiors of the powerful cosmic objects that may be the origins of high energy cosmic rays: supernovae, black holes, pulsars, active galactic nuclei and other extreme extragalactic phenomena. This award will fund the deployment of seven additional strings of photon sensors in the deep, clear Antarctic ice at the bottom center of IceCube, forming the IceCube Gen2 Phase 1 extension ('Phase 1').

The availability of a deep-ice drill presents several opportunities to enhance the existing IceCube infrastructure for research and education. Deep ice drills will also allow for the possibility of deploying next-generation optical sensor technology prototypes within the existing IceCube operations framework at the U.S. Amundsen-Scott South Pole Station, presenting new opportunities for training a new cohort of international students and young scientists throughout the instrumentation development, production, and field deployment. The combination of astrophysics and the extreme polar climate attracts wide popular interest.

The new strings will use multi-PMT Digital Optical Modules (mDOMs), providing better directionality and more than double the photocathode area per module, at lower cost per unit area, than traditional IceCube DOMs. The mDOMs will be tightly integrated into the existing IceCube data acquisition framework, at marginal added long-term maintenance and operations expense. The new instrumentation will dramatically boost IceCube's performance at the 5 GeV energy scale, yielding over an order of magnitude more statistics than current samples, and enabling IceCube to perform the world's best measurement of tau neutrino appearance and the world's most stringent test of unitarity in the tau sector of the PMNS (Pontecorvo-Maki-Nakagawa-Sakata) matrix. This matrix describes all known neutrino oscillation behavior, and deviations from unitarity would be evidence for new physics. The strings will feature new calibration devices that would allow to better model the optical properties of the ice, reducing systematic uncertainties in the tau neutrino appearance measurement and enhancing IceCube's already strong contribution to multimessenger astrophysics via improved reconstruction of the direction of high energy cascade events for searches of point sources and enhanced identification of PeV-scale tau neutrinos. High energy tau neutrinos are essentially guaranteed to be astrophysical in origin, and they are a unique probe of neutrino oscillation physics over ultra-long baselines, providing powerful complementarity with Phase 1's atmospheric tau neutrino appearance measurement at lower energies.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.