Neutrinos + Cosmic Rays

One of the primary research activities at our institute is the detection of ultra-high-energy neutrinos using radio observations. This plays a crucial role in advancing our understanding of extreme astrophysical objects.

Cosmic Neutrinos

About 100 trillion neutrinos pass through you every second. Most of them come from the Sun or the Earth’s atmosphere, but a few — those with much higher energies — are of cosmic origin. However, the source of these ultra-high-energy neutrinos is still not fully understood. Neutrinos interact so weakly with ordinary matter that detecting them requires extremely large detectors. The experimental group at LeCosPA (led by Prof. Jiwoo Nam) is involved in experiments at the South Pole that use the entire 14 million square kilometer Antarctic ice sheet as a detector. When a neutrino interacts with molecules in the ice, it produces secondary particles that leave a trace of blue light as they travel through the detector (see image below).

Credit: Nicolle Fuller(NSF/IceCube)


Members of LeCosPA are part of the 'Antarctic Impulsive Transient Antenna' (ANITA) experiment, a NASA long-duration balloon experiment that searches for the radio signals that are generated when ultra-high-energy neutrinos interact with the Antarcticice sheet. In 2018, ANITA saw an intriguing signal. During one of its flights, it detected high-energy particles coming from the ice, a kind of upside-down shower of cosmic rays. Despite its higher sensitivity, the IceCube experiment doesn’t see these events. The signal therefore cannot be from neutrinos that have traversed the Earth. They must have come from above and have reflected off the ice into the ANITA detector without leaving any signature in the deep ice where Ice Cube would have recorded them.


To solve the mystery of the anomalous ANITA events, members of LeCosPA have started construction of a new neutrino experiment: TAROGE (or 'Taiwan Astroparticle Radiowave Observatory for Geo-synchrotron Emissions'). The TAROGE experiment is an antenna array on the high mountains of Taiwan’s east coast. The antennas point toward the ocean to detect radio signals reflected off the ocean surface. Looking down from the high mountain, it can cover a vast area infield of view. TAROGE allows us to explore the detection of ultra-high-energy cosmic rays and earth-skimming tau neutrinos coming from near the horizon. A total of four stations, TAROGE-1 through TAROGE-4, have been installed in the Heping and NanAu. Recently, we have expanded the experiment to Antarctica, by installing the TAROGE-M experiment on the summit of Mt. Melbourne.


The IceCube experiment has established neutrino observations as a fascinating new discipline for the exploration of the universe. By observing neutrinos, we can obtain knowledge about regions of the cosmos where light is unable to provide useful information. In order to fully exploit the potential of this new window to the universe, the IceCube Collaboration is planning a significant expansion of the IceCube detector at the South Pole. Part of the upgrade will involve adding radio detection to the experiment, which is the expertise of the group at LeCosPA. We therefore expect members of LeCosPA to make significant contributions to IceCube-Gen2.

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