A dark matter detector designed and built by UC Davis undergraduate and graduate students is now undergoing trials at CERN. The device, a demonstration prototype for an experiment called FORMOSA, is currently installed in the forward region of the ATLAS detector, part of the Large Hadron Collider. 

“These students had a real, concrete impact on the whole prototype detector, rather than just being a small cog in a big machine,” said Matthew Citron, assistant professor in the UC Davis Department of Physics and Astronomy, who led the team. Particle accelerator projects like those at CERN typically involve teams of hundreds if not thousands of people. “Whereas for something that’s much smaller scale, like FORMOSA, it’s way easier for even an undergraduate student to make a huge impact on the experiment itself.”

Detecting dark matter

Dark matter is an invisible substance detectable only through its gravitational effects. It comprises just over a quarter of all the 'stuff' in the universe, according to current theories. 

“We have no evidence of what it actually is,” Citron said. “But as we theorize more and more, we’re learning that dark matter may not just be one particle but a whole sector that contains lots of different particles and they interact in different ways.”

Citron and his lab are specifically interested in millicharged particles, proposed subatomic particles that have a tiny fraction of an electron’s charge (somewhere between 0.1% and 10%). To collect evidence of their existence, Citron and colleagues designed FORMOSA, a particle detector meant to be sensitive enough to detect millicharged particles. 

The FORMOSA demonstrator was installed at the Large Hadron Collider in December, 2023. For the next two years, Citron's team will collect data to support building a full-scale instrument. 

Read more about the FORMOSA project and the people involved here.