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Possible Sighting of Dark Matter Lights Up Physics Community

• Rebecca Boyle via

Summertime may be the right time for unmasking dark matter. Researchers working on a dark matter experiment buried half a mile underground in a Minnesota mine say they’ve seen seasonally varying blips in electrical pulses that may be the telltale signs of WIMPs, or weakly interacting massive particles.

If they’re accurate, the new findings would back up previous research from an underground lab beneath a central Italian mountain, which has proved controversial for nearly a decade.

The new result comes from the Coherent Germanium Neutrino Technology (CoGeNT) experiment at Minnesota’s Soudan mine, where detectors are looking for the faintest interaction between WIMPs and atoms inside a germanium crystal. Researchers led by Juan Collar at the University of Chicago’s Kavli Institute for Cosmological Physics studied about 15 months of data — not very much, but they were interrupted by a fire in March.

They saw signs of a seasonal variation in the interactions between WIMPs and germanium crystals, according to the Kavli Institute. It’s not a WIMP signal per se, but it’s what you would expect to see from a WIMP signal, Collar said. WIMPs are thought to be particles of dark matter, which makes up about 23 percent of the universe.

It's hard to see these ineffable particles because they do not interact with the electromagnetic or strong nuclear forces. This is one reason why detectors are buried underground, breathing new life into old abandoned mines — thick rock layers shield the instruments from background radiation and cosmic rays that could block out a super-faint signal from a passing WIMP.

The detectors picked up an average of one WIMP interaction per day for 15 months, with a seasonal variation of 16 percent. (For a more thorough explanation of the results, read an extensive interview with Collar here.)

Along with echoing the previous Italian experiment, this fits with accepted theories of how Earth encounters dark matter clouds in our galaxy.


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