Going deep for detector R&D

Erik Ramberg

Sometimes you have to go to the ends of the Earth to get what you need. Last week for one Fermilab project this saying was more literal than figurative.

The DAMIC (Dark Matter In CCDs) experiment saw a very successful culmination of several years of detector research. The experiment employed a new technique for searching for the elusive particles that we think make up most of the matter in the universe—dark matter.

The latest episode for the DAMIC experiment played out in one of the more exotic laboratories in the world: the Sudbury Neutrino Observatory Lab, located 6,800 feet underground in an active nickel mine in Ontario, Canada. This laboratory provides the right conditions for DAMIC and other dark-matter experiments. The extreme depth filters out cosmic rays, which could mimic dark matter interactions, and the highly specialized SNOLAB crew keeps the laboratory in clean-room conditions.

DAMIC uses charged coupled devices—the CCDs that have been used for many years in digital cameras.. But these are not your average CCDs. They are the high-tech ones also used in the Dark Energy Camera, which Fermilab installed on the Blanco telescope in Chile. The detectors were developed and fabricated at Berkeley Lab and were tested and installed in the camera here at Fermilab. They are unusually thick (250 microns instead of the usual 30) and have low intrinsic noise levels, making them ideal for the long exposure times needed to search for the rare interactions expected for dark-matter particles.

Just down the tunnel from DAMIC, another Fermilab project, COUPP, operates two bubble chambers for dark-matter research. The smaller of the two (4 kilograms of liquid inside the bubble chamber) has been running for six months, while the 60-kilogram experiment is just now receiving its sensitive payload underground.

Both DAMIC and COUPP initially started as Fermilab PPD detector research and development projects with the goal of proving that the novel techniques they used could be expanded into large detector systems for the extremely challenging hunt for dark matter. Since that start, both projects have set world-class constraints on the potential interactions between dark and normal matter, and they have definitively proven that the techniques are sound.

Detector R&D, whether it is for dark-matter searches or for other research projects, contributes to the success of our laboratory by finding ways to work beyond the limitations of today’s technology. The members of our detector R&D group don’t always literally go to the ends of the Earth, but they do what it takes to make great experiments.

Erik Ramberg is assistant head for detector research.

Part of the DAMIC group stands by the newly installed detector. From left: Juan Estrada, Javier Tiffenberg, Herman Cease and Gustavo Cancelo, all from Fermilab. Photo courtesy of Erik Ramberg