Searching for cosmic neutrinos with radar technology

Searching for cosmic neutrinos with radar technology

First ever radar detection of particle track creates hope for breakthrough in search for cosmic neutrinos

Scientists have been searching for radar reflections from a particle track since the 1940s. A particle track occurs when an extremely high-energy cosmic particle collides in our atmosphere or, for example, with the Antarctic ice. An international scientific team led by VUB’s Prof. Krijn de Vries and Dr Steven Prohira of Ohio State University has now become the first ever to detect such a particle track, thereby demonstrating that radar technology can be used in the search for cosmic neutrinos. The results of this breakthrough have been published in Physical Review Letters.

Neutrinos have remained a mystery ever since they were first discovered more than fifty years ago. These elementary particles come from the furthest corners of the universe, are virtually massless and seldom interact with anything else. Very rarely, however, a high-energy neutrino collides with the polar ice.

The IceCube Neutrino Observatory, of which the VUB is a member, monitors a cubic kilometre of ice for neutrinos by looking for the light signals emitted during such a collision. But IceCube cannot detect all neutrinos – its strength lies in detecting neutrinos with energies below 10 billion electron volts (PeV). For neutrinos with higher energies, which are extremely rare, a much larger detector would be needed to detect one on reasonable time scale.

To detect neutrinos with higher energies, experiments have been conducted into the radio signals that neutrinos give off during a collision. Prof. de Vries and Dr. Prohira their team has now demonstrated for the first time that radar technology can be used for this purpose. By firing a beam of high-energy electrons at a target made of plastic, researchers at the SLAC National Accelerator Laboratory in California have succeeded in imitating the particle trace left by a neutrino during a collision in the Antarctic ice. While one antenna fired radio radiation at the plastic target, other antennas were used to keep watch. And indeed, the other antennas were able to detect the particle trail.

"With the test beam, we have shown that the principle works. The trace left by a neutrino with an energy between 10 and 100 PeV will obviously be different from the trace measured during this experiment, but based on our simulations, we think we will be still able to detect it if we send a more powerful radar wave into the ice," says Prof. de Vries, who works at the Elementary Particle Physics research group at the Vrije Universiteit Brussel.

Next year, the team hopes to build a rig to test the radar method in Antarctica, as a stepping stone to creating a detector that can measure actual neutrino traces.

"The kind of neutrinos we will be able to detect with radar technology will be able to tell us more about the extremely energetic astronomical phenomena in our universe. This may even bring new physics to light," says Prof. de Vries.



Prof. Krijn de Vries

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