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lecture hall with a lot of students © Jürgen Huhn​/​TU Dortmund
Cosmic Neutrino Detector

Hundreds of new ‘eyes’ buried in the Antarctic ice

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The photo shows how the glass ball is lowered into the borehole. © NSF​/​Yuya Makino
View into the borehole into which one of hundreds of pressure-resistant glass spheres with photomultiplier tubes is lowered.
Since 2009, researchers have been using the IceCube Neutrino Observatory at the South Pole to search for cosmic ray sources. Now, during the Antarctic summer, the team has taken advantage of the conditions to install an important upgrade. Fifty-one scientists and technicians successfully deployed 670 sensors and calibration devices in the Antarctic ice. These new components will significantly improve the detector’s capability at lower neutrino energies. Physicists from TU Dortmund University and Ruhr University Bochum were involved in the IceCube upgrade, and two TU researchers were present on site.

The current upgrade is an important milestone on the path toward the future IceCube-Gen2 facility. It is expected to significantly increase sensitivity and open up new scientific opportunities. Researchers at TU Dortmund University are working closely with partners from Ruhr University Bochum in the IceCube consortium; the two universities are currently applying together as Ruhr Innovation Lab in the Excellence Strategy. A total of nine German universities and the two research institutes KIT and DESY are members of the consortium.

The photo shows the people who were involved in the upgrade on site. © IceCube
A total of 51 scientists and technicians buried 670 new sensors and calibration devices in the Antarctic ice, including Johannes Werthebach and Dr. Alicia Fattorini from TU Dortmund University.

Hundreds of glass spheres 2,600 meters deep in the ice

The German partners have jointly contributed to the design, testing, and deployment of the new sensor technology. A pressure-resistant glass sphere, called a multi-PMT digital optical module (mDOM), houses multiple photomultiplier tubes (PMTs). These PMTs record the faint flashes of light produced when neutrinos occasionally interact with matter in the ice. The modules are deployed like pearls on a string: long cables carrying more than 100 devices were lowered into individual boreholes up to 2,600 meters deep. There, the ice serves as both the target and the detection medium for the ghostly cosmic particles. Alongside the new optical modules, the upgrade also included new calibration devices and cameras. These instruments provide controlled reference measurements and in-situ monitoring, which helps characterize the optical properties of the ice and the detector response under real operating conditions more accurately.

A red illuminated steel structure in the snow under a night sky with a lot of stars.
The above-ground laboratory of the neutrino detector.
Selfie of man in red jacket standing outside in snow with scarf, eyelashes and eyebrows covered with ice
Johannes Wertebach spent a whole year at the IceCube neutrino observatory in Antarctica in 2018.
A two-story building with four side wings in the snow under a night sky with green glowing auroras.
Scientists live at the Amundsen-Scott South Pole Research Station during their stay.

Around five thousand PMTs were tested and calibrated at TU Dortmund University as part of Johannes Werthebach’s Ph.D. thesis before being forwarded for integration and assembly into complete mDOMs. Scientists from Ruhr University Bochum contributed to improving the ice characterization through a new camera system. TU physicist Johannes Werthebach and Dr. Alicia Fattorini participated in the deployment at the South Pole. Werthebach worked specifically on the upgrade and supported critical installation steps, such as freezing the glass modules in the boreholes. Fattorini, an IceCube winterover, helped ensure the observatory's continuous year-round operation under extreme conditions.

Looking ahead, the newly installed calibration devices and camera systems will reduce systematic uncertainties and improve the reconstruction of neutrino events. These improvements will enhance future measurements and enable the improved reconstruction and reanalysis of the complete IceCube data set already collected. This will strengthen IceCube’s overall physics reach and lay important groundwork for the next-generation IceCube-Gen2 observatory.

About the Ruhr Innovation Lab

Ruhr University Bochum and TU Dortmund University, which currently apply together as the  Ruhr Innovation Lab in the Excellence Strategy, work closely on issues that help to develop a sustainable and resilient society in the digital age. At the same time, collaborations in basic research are opening up new insights into the building blocks of our world.

Neutrinos emerge from various kinds of nuclear reactions. They are nearly massless, carry no electrical charge, and only very rarely interact with matter. However, within the last decades, scientists have figured out ways to detect neutrinos using massive amounts of dense material – such as the ice sheet of the Antarctic – learning much about the particles. When neutrinos interact with matter, a heavier partner particle emerges, as well as a brief flash of light. Scientists use photomultiplier tubes (PMTs) to amplify the light into electrical signals that can be detected. By this method, neutrino observatories around the world have made these ghostly particles into messengers that relay information about distant regions of the cosmos.

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