Deep in a Minnesota Mineshaft

By Joseph Salvo

Bullet Clusters are regions where collisions between two galactic clusters have caused a separation of dark and baryonic matter.
Bullet Clusters are regions where collisions between two galactic clusters have caused a separation of dark and baryonic matter.

Deep in a Minnesota mineshaft, MIT researcher Enectali Figueroa-Feliciano searches for the universe’s ghostly building blocks. Figueroa, known to his colleagues as “Tali Figueroa,” is a leading expert in the Cryogenic Dark Matter Search experiment (CDMS), a project that analyzes collisions between atomic nuclei and unimaginably small particles called WIMPs (Weakly Interacting Massive Particles).

Why should federal funds be spent on seemingly insignificant quantum constructs that pass through matter like phantoms? Figueroa, in his talk last Friday at Northwestern University’s Evanston campus, explained that the mechanisms underlying WIMPs and their interactions are leading explanations for the mysterious phenomenon of “dark matter,” an unknown substance that is believed to form an estimated 25% of the universe.

“We have to come to grips with the dark-side of the universe,” joked Figueroa, as he showed a slide of Darth Vader.

According to Figueroa, WIMP collisions are few and far between. In a normal banana, for example, there are an estimated average of 100 radioactive collisions, or “events,” every second. In comparison, the average number of WIMP events is just one per year. Detecting these rare events requires crystals that vibrate easily when they come in contact with the almost massless WIMPs. The vibrations from these collisions, called phonons, are detected by highly sensitive instruments, which are kept underground to diminish interference from background radiation.

Figueroa is optimistic about what the future holds for dark matter research. A new CDMS detector, called SuperCDMS SNOLAB, will soon be built, transforming dark matter research. SNOLAB will use both Germanium and Aluminum crystals, will filter out background radiation 100 times better than its predecessors, will operate at a lower temperature, and is expected to provide higher resolution imaging. In addition, Figueroa has been working with NASA to put an X-ray spectrometer in space. Vibration testing was carried out in 2013, and the rocket is expected to launch sometime next year. Both these developments will catapult the field in new directions, as more mysteries are revealed.

In spite of the difficulties inherent in studying particle physics, Figueroa argues beauty inherent in studying dark matter.

“It spans an enormous range of scales,” he said, “from the largest parts of the universe down to the subatomic realm.” Giles Novak, a professor in the Northwestern Physics and Astronomy Department, agreed, stating that dark matter’s nature is one of the important issues in physics for scientists to resolve.

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