Hunting for the Axion with a Huge Magnet

Imagine a ten-meter-long magnet that is operated at around minus 270°C and that sits on a moving platform, allowing it to track the Sun through the sky for 12 hours a day. With the DFG having signed off funding, the physicists in the BabyIAXO project can now start putting it in motion. “This is the largest dipole magnet that’s ever been constructed in particle physics,” says a happy Professor Matthias Schott, coordinator of the research proposal and Speaker for the Matter Transdisciplinary Research Area at the University of Bonn. “The magnet is the beating heart of the experiment and is what makes BabyIAXO possible in the first place.”

The system behind BabyIAXO is really quite special: The superconducting magnet has to be operated at temperatures close to absolute zero to achieve the necessary magnetic field strengths. A unique design is also called for, because the magnet has to tilt a long way up and down in order to follow the Sun. The system is to be built at the research centerDESY in Hamburg.

From a “baby” to a full-grown magnet system

As the name suggests, BabyIAXO represents an intermediate stage on the journey to an even bigger, “full-grown” magnet system, namely the International Axion Observatory (IAXO). This is set to be twice as large, i.e. with a 20-meter-long magnet, making it the biggest helioscope experiment planned in the hunt for the axion. The telescope will study the Sun at an unprecedented level of sensitivity, some 10,000 times more efficiently than the most powerful helioscope employed to date, hopefully enabling it to finally provide proof of the axion’s existence. “IAXO will have eight measuring stations, each of which can be kitted out with various telescopes and detectors,” says IAXO Collaboration Board Chair Professor Klaus Desch from the University of Bonn. “This will let us look for axions with a variety of properties and capture as wide a range of potential axions as possible.”

Professor Julia K. Vogel from TU Dortmund University, IAXO’s Deputy Spokesperson, adds: “We first have to create the technologies and instruments that IAXO will need ourselves. This will require intensive research and development as well as extensive experimental testing, and BabyIAXO marks a crucial step on this journey.”

The axion: a solution to a fundamental problem in the Standard Model

Some may wonder why so much money and effort are being invested in the search for a hypothetical elementary particle. Physicists, however, need no convincing: proving the existence of the axion would solve one of the fundamental puzzles of the Standard Model of particle physics, namely the “strong CP problem”.

The problem can be understood as follows: according to the known laws of nature, many physical processes should remain unchanged if particles are replaced by their antiparticles while the system is simultaneously “flipped,” as if viewed in a mirror. Physicists know that the weak interaction violates this “CP symmetry.” The theory of the strong interaction, which binds quarks into protons and neutrons, also allows for such CP violation. “Despite decades of experimenting, however, physicists have never succeeded in actually observing such a violation,” Schott explains. To resolve this contradiction, in 1977 Roberto Peccei and Helen Quinn postulated the axion, a hypothetical elementary particle with an extremely small mass that interacts extraordinarily feebly with ordinary matter. “These properties also make the axion a very good candidate for dark matter,” Desch adds. In other words, physicists have two compelling reasons for running experiments to hunt for signs of its existence.

Institutions involved and funding secured:

Twenty universities and research institutions from all over the world are involved in IAXO. As part of its major instrumentation programme, the DFG has approved the construction of a magnet system costing €6 million for the BabyIAXO project. Of this amount, €3 million will be provided by the DFG itself, €2.4 million by the state of North Rhine-Westphalia and a further  €600,000 jointly by the University of Bonn, the University of Siegen and TU Dortmund University as part of the “Color meets Flavor” Cluster of Excellence.

International Axion Observatory (IAXO)

Cluster of Excellence Color meets Flavor

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