Dark matter more elusive than ever as scientists admit detector has failed to find mystery particle

Via telegraph.co.uk by Sarah Knapton

Dark matter is said to make up four fifths of the mass of the universe, but finding it is another matter entirely.

A team of scientists, including University College London, have turned off their £7 million ultra-sensitive detector after failing to pick up any hint of the most elusive material in the cosmos.

Despite probing ‘unexplored regions of parameter space’ researchers were left scratching their heads by the stubborn reluctance of dark matter to step in to the light.

“Though a positive signal would have been welcome, nature was not so kind,” Dr Cham Ghag, of UCL.


Scientists think large quantities of dark matter must exist because of the way its gravity affects the rotation of galaxies and bends light.

But although it appears to play a key role in binding together and shaping the cosmos, dark matter cannot be seen with conventional telescopes or instruments.

To find it, scientist built The Large Underground Xenon (Lux) experiment beneath a mile of rock in a former gold mine in South Dakota.

Placed within a tank filled with 72,000 gallons of high purity water, it was designed to spot tiny flashes of light emitted as dark matter particles collided with atoms of xenon.

But results from the detector's final 20-month run, which ended in May this year, revealed no sign of the elusive particles.

Lux was looking for weakly interacting massive particles (Wimps), thought to be the best theoretical candidate for dark matter.

According to the Wimp theory, billions of ghostly dark matter particles pass unnoticed through us every second.

Despite the lack of success, the scientists are planning a detector with 70 times more sensitivity than Lux may yet succeed in finding the particles.

Leading Lux investigator Professor Rick Gaitskell, from Brown University in the US, said: "Lux has delivered the world's best search sensitivity since its first run in 2013.

"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.

"It would have been marvellous if the improved sensitivity had also delivered a clear dark matter signal. However, what we have observed is consistent with background alone."

The news that Lux had found no trace of dark matter was announced at IDM 2016, an international meeting of dark matter experts taking place in Sheffield.

“We worked hard and stayed vigilant over more than a year and a half to keep the detector running in optimal conditions and maximize useful data time,” said Simon Fiorucci, a physicist at Berkeley Lab and Science Coordination Manager for the experiment.

“The result is unambiguous data we can be proud of and a timely result in this very competitive field - even if it is not the positive detection we were all hoping for.”

A new Wimp hunting experiment, Lux-Zeplin (LZ), is due to replace Lux at the Sanford Underground Research Facility.

It will have a much bigger 10-tonne liquid xenon detector.

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