In the era of precision cosmology, research often means big science: large observatories, highly complex instruments, international collaborations and substantial funding. Yet even in such an advanced field, progress is still possible — including in the search for elusive dark matter — through more agile approaches, driven by small teams and young researchers, supported by institutions and a good dose of ingenuity.
In a paper just published in the Journal of Cosmology and Astroparticle Physics (JCAP), a group of then-undergraduate students from the University of Hamburg built a cavity detector to search for axions — among the most promising candidates for dark matter — and set new experimental limits on their properties. The result was achieved with relatively limited resources, showing that even small-scale experiments can make a meaningful contribution to one of the most open challenges in modern physics.
Funding for students
The project was made possible through a student research grant provided by the University of Hamburg via the Hub for Crossdisciplinary Learning, which supports independent research initiatives.
"We were kind of embedded in the research group of the MADMAX dark matter experiment," explains Nabil Salama, one of the authors of the study, currently pursuing an M.Sc. in Physics at the University of Hamburg. "MADMAX carries out a similar experiment on a much larger and more complex scale, and we benefited from their expertise and support."
"We are very grateful for this help," he adds, "and also to the University of Hamburg and the Quantum Universe Cluster of Excellence, which provided funding, access to key equipment such as the magnet, and invaluable support from researchers."
Searching for dark matter
"The benefit of working with dark matter, or axions, is that we expect it to be present everywhere in our galaxy," says Agit Akgümüs, first author of the study with Salama, currently pursuing an M.Sc. in Mathematical Physics at the University of Hamburg. "So essentially, no matter where you perform the experiment, you have some dark matter on your hand you can do experiments with."
The funding was first used to build the experimental setup, starting with a resonant cavity made from highly conductive materials, along with the necessary electronics, cabling, supports and measurement instruments. "The detector we built is essentially the simplest version of a cavity detector for dark matter," says Salama.
The team did not work entirely from scratch: in addition to the funding, they relied on existing infrastructure and equipment provided by the university and collaborating research groups.
The experiment was then tested, calibrated and operated to collect data for analysis.
"We reduced very complex experiments to their essential components," says Salama. "The result is a less sensitive setup, limited to a small search window, but still capable of producing new scientific data."
No signal found, new limits set
"The search for axions involves exploring a wide range of possible parameters," adds Akgümüs. "Our experiment covers only a small region, with limited sensitivity, but it still helps narrow down the possibilities. To actually find the particle, we need either much larger experiments or many different ones, each probing a specific region."
At the end of the data-taking phase, the team did not observe any signal attributable to axions. Rather than a failure, this is a meaningful scientific result: it allows researchers to exclude the presence of axions with certain properties within the explored mass range, particularly those with stronger interactions with photons. In this way, the study helps narrow the parameter space and guide future searches.
"I think the point of our experiment is that things can be done on a smaller scale," says Salama. Akgümüs adds: "Our results are naturally more limited than those of larger experiments. Performance scales with resources and complexity. However, we have shown that it is possible to reduce these setups to a much smaller scale — even to projects developed almost independently by students — while still producing real scientific data."
During the peer-review process of the paper, a referee made a particularly notable comment, Salama recalls. According to the referee, once the axion is discovered and its properties — especially its mass — are known, experiments of this kind could become far more accessible, potentially even suitable for teaching laboratories. "We were told that setups like ours could one day become standard student lab experiments," says Salama. "In a way, we may have anticipated that future, showing that it is already possible to build and operate such an experiment on a small scale."
The paper "A New Limit for Axion Dark Matter with SPACE" by M. A. Akgümüs, N. Salama, J. Egge, E. Garutti, M. Maroudas, L. H. Nguyen, and D. Leppla-Weber has been published in the Journal of Cosmology and Astroparticle Physics (JCAP).
