April 13, 2024

New research uses ‘parabolic’ coaxial antenna to search for dark matter

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A rendering of the BREAD design. The “Hershey’s Kiss”-shaped structure channels potential dark matter signals to the copper-colored detector on the left. The detector is compact enough to fit on a table. Credit: BREAD Collaboration

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A rendering of the BREAD design. The “Hershey’s Kiss”-shaped structure channels potential dark matter signals to the copper-colored detector on the left. The detector is compact enough to fit on a table. Credit: BREAD Collaboration

One of the great mysteries of modern science is dark matter. We know that dark matter exists thanks to its effects on other objects in the cosmos, but we have never been able to see it directly. And it’s no small feat – scientists currently think it represents about 85% of the entire mass of the universe.

A new experiment from a collaboration led by the University of Chicago and Fermi National Accelerator Laboratory, known as the Broadband Reflector Experiment for Axion Detection or BREAD, has released its first results in the search for dark matter in a study published in Physical Review Letters. Although they didn’t find dark matter, they eased restrictions on where it could be and demonstrated a unique approach that could speed up the search for the mysterious substance, with relatively little space and cost.

“We’re really excited about what we’ve been able to do so far,” said UChicago Assoc. Prof David Miller, co-leader of the experiment alongside Fermilab’s Andrew Sonnenschein, who originally developed the experiment’s concept. “There are many practical advantages to this design and we have already demonstrated the best sensitivity to date at this 11-12 gigahertz frequency.”

“This result is a milestone for our concept, demonstrating for the first time the power of our approach,” said Stefan Knirck, a Fermilab postdoctoral researcher and lead author of the study, who led the construction and operation of the detector. “It’s great to do this kind of creative science at a tabletop scale, where a small team can do everything from experiment construction to data analysis, but still have a big impact on modern particle physics.”

‘Something is there’

When we look around the universe, we can see that some kind of substance exerts enough gravity to attract stars and galaxies and pass light, but no telescope or device has ever directly detected the source – hence the name “dark matter”.

However, since no one has ever seen dark matter, we don’t even know exactly what it might look like or even exactly where to look for it. “We are very confident that something exists, but it can take many, many forms,” Miller said.

Scientists have mapped out several of the most likely options for locations and forms of observation. Typically, the approach has been to build detectors to thoroughly search a specific area (in this case, a set of frequencies) in order to rule it out.

But a team of scientists explored a different approach. Its design is “wideband,” which means it can search a wider range of possibilities, albeit with slightly less precision.

“If we think of it like a radio, the search for dark matter is like tuning the dial to look for a specific radio station, except there are a million frequencies to check,” Miller said. “Our method is like scanning 100,000 radio stations rather than a few minutely.”

A proof of concept

The BREAD detector looks for a specific subset of possibilities. It was built to look for dark matter in the form known as “axions” or “dark photons” – particles with extremely small masses that could be converted into visible photons in the right circumstances.

Thus, BREAD consists of a metal tube containing a curved surface that captures and channels potential photons to a sensor at one end. The whole thing is small enough to fit in your arms, which is unusual for this type of experiment. In the full-scale version, BREAD will be placed inside a magnet to generate a strong magnetic field, which increases the chances of converting dark matter particles into photons.

To prove the principle, however, the team performed the experiment without magnets. The collaboration ran the prototype device at UChicago for about a month and analyzed the data.

The results are very promising, showing very high sensitivity at the chosen frequency, the scientists said.

Since the results published in Physical Review Letters were accepted, BREAD has been moved inside a repurposed MRI magnet at Argonne National Laboratory and is collecting more data. Its eventual headquarters, at the Fermi National Accelerator Laboratory, will use an even stronger magnet.

“This is just the first step in a series of exciting experiments we are planning,” said Sonnenschein. “We have many ideas to improve the sensitivity of our axionic search.”

“There are still many open questions in science and enormous room for creative new ideas to address these questions,” Miller said. “I think this is a really striking example of these kinds of creative ideas – in this case, collaborative, impactful partnerships between smaller-scale science at universities and larger-scale science at national laboratories.”

The BREAD instrument was built at Fermilab as part of the lab’s detector research and development program and then operated at UChicago, where the data for this study was collected. UChicago graduate student Gabe Hoshino led the detector’s operation, along with graduate students Alex Lapuente and Mira Littmann.

Argonne National Laboratory maintains a magnetic facility that will be used in the next stage of the BREAD physics program. Other institutions, including SLAC National Accelerator Laboratory, Lawrence Livermore National Laboratory, Illinois Institute of Technology, MIT, Jet Propulsion Laboratory, University of Washington, Caltech, and University of Illinois at Urbana-Champaign, are working with the UChicago and Fermilab in R&D for future versions of the experiment.

More information:
Stefan Knirck et al, First results from a broadband search for dark matter from dark photons in the range 44 to 52 μeV with a coaxial parabolic antenna, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.132.131004

Diary information:
Physical Review Letters

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