The world's most sensitive instrument deployed in the search for dark matter is now 20 times more sensitive thanks to an upgrade involving improved calibration techniques, scientists participating in the project say.
Those techniques are all designed to reduce background interference with the search for mysterious invisible particles thought to make up 85 percent of all the matter in the universe.
The instrument at the center of the Large Underground Xenon experiment, or LUX, consists of a large container of liquid xenon sitting almost a mile underground in a former gold mine in South Dakota's Black Hills.
Photon detectors arrayed around the vat of liquid xenon are poised to catch the tiny flashes of light expected when the invisible particles known as WIMPs — weakly interacting massive particles — strike xenon nuclei.
WIMPS are considered leading candidates for dark matter.
"We have improved the sensitivity of LUX by more than a factor of 20 for low-mass dark matter particles, significantly enhancing our ability to look for WIMPs," says Rick Gaitskell, a physics professor at Brown University working on the LUX experiment.
Scientists believe dark matter exists — even if it is invisible — because the effects of its mass, and therefore its gravity, can be seen on the rotation of galaxies and the bending of light traveling across the universe.
Experiments on Earth have as yet been unable to detect dark matter, likely because its local interactions are both extremely weak and extremely rare, leading to the search for the elusive WIMPs.
"We look for WIMPs produced in the Big Bang that are still around, up to very high masses — we have the best sensitivity of any experiment to date for WIMP masses above four times that of a proton," says LUX researcher and physics professor Daniel McKinsey from the University of California, Berkeley.
"We haven't yet observed dark matter interactions, but the search goes on," he says.
Recent testing after the new calibrations, intended to filter out false interaction resulting in collisions among cosmic and gamma rays, has proved the LUX detector has become more sensitive than ever, the researchers say.
"These calibrations have deepened our understanding of the response of xenon to dark matter, and to backgrounds," explains Alastair Currie, a researcher with LUX from Imperial College London. "This allows us to search, with improved confidence, for particles that we hadn't previously known would be visible to LUX."
The scientists have reported their latest efforts in a study set to appear in the journal Physical Review Letters.
