LUX dark matter results confirmed

A new calibration technique fired neutrons directly into the Large Underground Xenon (LUX) dark matter detector, increasing calibration accuracy by a factor of 10. 

Analysis based on the calibration confirms that if "low-mass" dark matter particles had passed through the detector during its initial run, Large Underground Xenon would have seen them. 

Credit: Matt Kapust/Sanford Underground Research Facility

A new high-accuracy calibration of the LUX (Large Underground Xenon) dark matter detector demonstrates the experiment's sensitivity to ultra-low energy events.

The new analysis strongly confirms the result that low-mass dark matter particles were a no-show during the detector's initial run, which concluded last summer.

The first dark matter search results from LUX detector were announced last October.

The detector proved to be exquisitely sensitive, but found no evidence of the dark matter particles during its first 90-day run, ruling out a wide range of possible models for dark matter particles.

Previous experiments had detected potential signatures of dark matter particles with a very low mass, but LUX turned up no such signal.

This latest work was focused on demonstrating the high sensitivity of LUX to potential signals in the search for those low-mass particles.

Rick Gaitskell

"The new calibration improved our calibration accuracy by about a factor of 10," said Rick Gaitskell, professor of physics at Brown University and co-spokesperson for LUX.

"It demonstrates that our first dark matter search result, which showed no sign of low-mass particles, is absolutely robust."

The results of the new analysis were presented Wednesday, Feb. 19, 2014, at the Lake Louise Winter Institute in Alberta, Canada, by James Verbus, a graduate student at Brown who led the new calibration work.

Dark matter is thought to account for about 80 percent of the mass of the universe. Though it has not yet been detected directly, its existence is a near certainty among physicists.

Without the gravitational influence of dark matter, galaxies and galaxy clusters would simply fly apart into the vastness of space.

It's not clear exactly what dark matter is, but the leading idea is that it consists of subatomic particles called weakly interacting massive particles (WIMPs).

WIMPs are thought to be practically ubiquitous in the universe, but because they interact so rarely with other forms of matter, they generally pass right through the earth and everything on it without anyone knowing it.

The LUX is designed to detect those rare occasions when a WIMP does interact with other forms of matter.

The detector consists of a third of a ton of supercooled xenon in a tank festooned with light sensors, each capable of detecting a single photon at a time.

As WIMPs pass through the tank, they should, on very rare occasions, bump into the nucleus of a xenon atom.

Those bumps cause the nucleus to recoil, creating a tiny flash of light and an ion charge, both of which are picked up by LUX sensors.

The detector is more than a mile underground at the Sanford Underground Research Facility in South Dakota, where it is shielded from cosmic rays and radiation that might interfere with a potential dark matter signal.

This latest work was an entirely new way of calibrating the detector to recognize a WIMP signal.