Searching for the Axion with a Giant Magnet
The special, ten-meter-long magnet is a technical masterpiece: Thanks to a movable platform, it can track the sun for twelve hours a day, thereby aiding the search for a previously undiscovered elementary particle, the axion. Thanks to joint funding totaling six million euros from the German Research Foundation (DFG), the state of North Rhine-Westphalia, and the Cluster of Excellence “Color meets Flavor,” the physicists working on the “BabyIAXO” project can now build the necessary magnet system. “This is the largest dipole magnet ever built for particle physics,” says Prof. Dr. Matthias Schott, coordinator of the research proposal and spokesperson for the Transdisciplinary Research Area (TRA) “Matter” at the University of Bonn. “The magnet is the heart of the experiment and is what makes BabyIAXO possible in the first place.” The system is being built at the German Electron Synchrotron (DESY) in Hamburg by the Cluster of Excellence “Color meets Flavor” of the Universities of Bonn, Siegen, and Dortmund. The BabyIAXO system is quite a feat: The superconducting magnet must be operated at approximately -270 degrees Celsius to achieve the required magnetic field strengths. In addition, a special design is necessary because the magnet must tilt far upward and downward to track the sun.
At the Center for Particle Physics at the University of Siegen, the focus of IAXO research is on developing a detector system in which naturally occurring radioactive impurities are drastically reduced. Prof. Dr. Ivor Fleck, head of the Siegen research group, comments: “The high purity requirements for the readout system are necessary because we expect fewer than ten signal events from the Sun per year. The radioactivity present in conventional materials generates more than a thousand times as many events in our detector, so we would not be able to detect the signals from the axions. Through the BabyIAXO experiment, we have the opportunity to participate in the discovery of an elementary particle—the axion—and to test analysis methods that we can later apply in the large-scale IAXO project.”
From “Baby” to a Full-Scale Magnetic System
As the name suggests, “BabyIAXO” is an intermediate step on the path to a larger “full-scale” magnet system: The International Axion Observatory (IAXO) is planned to be twice as large—with a 20-meter-long magnet—making it the largest helioscope experiment ever planned in the search for axions. The telescope will study the Sun with unprecedented sensitivity: about 10,000 times more efficient than the most powerful helioscope to date. It is thus expected to finally provide proof of the axion. “IAXO will have eight measurement stations that can be equipped with various telescopes and detectors,” says IAXO Collaboration Board Chair Prof. Dr. Klaus Desch of the University of Bonn. “This will allow us to search for axions with different properties and cover as wide a range of possible axions as possible.”
“We first have to develop the technologies and instruments that IAXO requires ourselves,” adds IAXO Deputy Spokesperson Prof. Dr. Julia Vogel of the Technical University of Dortmund. “This requires intensive research and development work as well as extensive experimental testing. BabyIAXO is an important step on this path.”
The Axion: Solution to a Fundamental Problem of the Standard Model
But why go to such great lengths to find a hypothetical elementary particle? For physicists, this question doesn’t arise: If they could detect the axion, they would have solved a fundamental problem of the Standard Model of particle physics, the so-called “strong CP problem.” What this means is the following: According to the known laws of nature, many physical processes should remain unchanged if particles are replaced by their antiparticles and the system is simultaneously spatially reflected. Physicists know that this “CP symmetry” is violated in the weak interaction. The theory of the strong interaction, which binds quarks into protons and neutrons, also allows for such a CP violation. “Despite decades of experiments, however, physicists have not been able to observe such a violation,” explains Prof. Matthias Schott. To resolve this contradiction, Roberto Peccei and Helen Quinn postulated the axion in 1977. This is a hypothetical elementary particle with an extremely low mass that interacts only very weakly with ordinary matter. “These properties also make the axion a very good candidate for dark matter,” says IAXO Collaboration Board Chair Klaus Desch. So there are two good reasons why physicists worldwide are searching for experimental evidence of its existence.
Participating Institutions and Funding:
Twenty universities and research institutes worldwide are participating in the International Axion Observatory (IAXO). With this major equipment grant, the DFG has approved the construction of a magnet system for the preliminary project “BabyIAXO” in the amount of six million euros: 3 million euros come from the DFG; 2.4 million euros are provided by the state of North Rhine-Westphalia; the universities of Bonn, Siegen, and Dortmund are contributing a total of 600,000 euros as part of the “Color meets Flavor” Cluster of Excellence.
