Scientists using the ultra-sensitive LUX dark-matter detector report that their search has come up negative after 20 months.

LUX is buried underneath a mile of rock, and has not been able to detect dark matter. However this latest search does allow scientists to narrow down the possible characteristics of the substance, writes Sarah Lewin for Space.com.

Dark Matter
Image source: Wikimedia Commons

Researchers reveal findings at UK conference

Scientists revealed their results on July 21 at the 11th Identification of Dark Matter Conference (IDM2016) in Sheffield, England. The conference brings together researchers who are searching for information on dark matter, the strange material that theoretically accounts for over 80% of the mass in the universe.

“LUX has delivered the world’s best search sensitivity since its first run in 2013,” Rick Gaitskell, a physicist at Brown University and co-spokesman for LUX, said in a statement. “With this final result from the 2014 to 2016 search, the scientists of the LUX Collaboration have pushed the sensitivity of the instrument to a final performance level that is four times better than the original project goals.”

LUX stands for Large Underground Xenon dark-matter experiment. The device is located in a former gold mine in South Dakota, which is now known as the Sanford Underground Research Facility. It is buried a mile underground in a 272,500 liter tank of purified water, where a 1.8 meter tank contains 302 kilograms of frigid liquid xenon.

No signal detected in latest test

The xenon is meant to light up when a dark matter particle hits one of its atoms. The device is buried to stop any other particles causing a false positive, but the lack of results shows that nothing with the right properties hit the xenon.

“It would have been marvelous if the improved sensitivity had also delivered a clear dark-matter signal,” Gaitskell said. “However, what we have observed is consistent with background alone.”

Dark matter has never been detected directly, but it plays a significant role in the universe. Scientists have been able to observe extra matter in the universe due to the way that galaxies rotate and light bends as it passes near them. LUX is made to search for weakly interacting massive particles (WIMPs), which scientists believe could be dark matter. WIMPS would be able to get through the rock and other materials and hit the xenon.

Who will find dark matter first?

No results were detected, which suggests that WIMPs cannot affect ordinary matter within a certain range. Scientists now know more about the characteristics of dark matter without having actually detected it.

Other experiments are also underway in the hunt for dark matter. Among the other experiments are COUPP-60, the XENON Dark Matter Project in Italy, and the Super Cryogenic Dark Matter Search (SUPERCDMS) which use similar techniques.

One experiment at the Large Hadron Collider is attempting to create dark matter before detecting its signal.

“We viewed this as a David and Goliath race between ourselves and the much larger Large Hadron Collider (LHC) at CERN in Geneva,” Gaitskell said. “LUX was racing over the last three years to get first evidence of a dark-matter signal. We will now have to wait and see if the new run this year at the LHC will show evidence of dark-matter particles, or if the discovery occurs in the next generation of larger direct detectors.”

LUX scientists are also working on a next generation detector. The LUX-Zeplin will be 70 times as sensitive as LUX.