The nature of dark matter is probably one of the most pressing questions in modern physics. Although the existence of dark matter, due to many astrophysical and cosmological observations of its gravitational influence, is difficult to refute, an experimental detection in the laboratory is still missing. Particles called axions could solve the dark matter mystery, and scientists have now founded the MADMAX collaboration (MAgnetized Disc and Mirror Axion eXperiment) that uses a novel experimental approach to detecting them. MADMAX will be located in the experimental hall of a former HERA experiment and will complement the ALPS II experiment. ALPS II is currently under construction and will look for axion-like particles in the HERA accelerator tunnel. DESY also participates in the IAXO proposal that will look for solar axions.

The members of the newly founded MADMAX collaboration at the experiment's future location at DESY in Hamburg. (Photo: M. Grefe/University of Hamburg)

However, such particle candidates have not been found in exeriments so far. This leads to the resurgence of a long-established hypothesis that was introduced independently of the dark-matter problem in order to solve another fundamental problem of particle physics: the question of the unexplained symmetry between matter and antimatter in the strong interaction, also known as quantum chromodynamics (QCD). This hypothesis predicts the existence of so called axions that could also solve the dark-matter problem.

There are several experiments and initiatives that search for axions as dark-matter candidates. None of these experiments, however, is sensitive to axions in the mass range between 40 and 400 microelectronvolts. This mass range is predicted in models assuming that axions were produced after the inflationary phase of the universe..

In 2013, an idea was published that could make it possible for experiments to become sensitive enough in this theoretically well motivated mass range to detect dark matter axions. For this purpose, up to 80 discs from a material with a high refractive index with a diameter of one metre are to be placed into a magnetic field with a strength of about 10 Tesla. With the correct adjustment of the disc spacings this could result in resonant conversion of axions into microwaves (photons). These could then be detected with extremely sensitive detectors.

Scientists from several research institutes have joined together to facilitate such an experiment: On 18 October 2017, the MADMAX Collaboration was officially formed. Apart from the group at the Max Planck Institute for Physics, where the basic concept has been developed, the MADMAX collaboration consists if research groups of the universities of Aachen, Hamburg and Tübingen, the University of Zaragoza in Spain, the French Research Institute for Fundamental Laws of the Universe CEA-IRFU in Saclay and Deutsches Elektronen Synchrotron (DESY) in Hamburg.

The researchers of the newly founded MADMAX collaboration are planning a finding phase in which they plan to very that the concept is feasible: the theoretical-phenomenological considerations that led to the concept have to be critically questioned. Parallel to these, first design studies on the feasibility of a suitable magnet and the necessary mechanics are carried out.

If these studies turn out satisfactory, a smaller prototype of the experiment will be built by 2021. Even this setup might provide a sensitivity, which allows scientists to search for previously untestable exotic dark matter particles.

With the final stage of the MADMAX experiment it should then be possible to cover an important parameter range for axions, which is predicted if axions are the dark matter.

Further Information: MADMAX-Homepage