LUX, now with more sensitivity

The Large Underground Xenon (LUX) dark matter experiment, located on Sanford Lab's 4850 Level is already the most sensitive dark matter detector in the world. Now, researchers have improved the detector's sensitivity level, dramatically increasing its ability to find WIMPs (weakly interacting massive particles). 

Using a new set of calibration techniques, the research re-examines data collected during LUX's first three-month run in 2013, and helps rule out the possibility of dark matter detections at low-mass ranges where other experiments had previously reported potential detections. 

"It is vital that we continue to push the capabilities of our detector in the search for elusive dark matter particles," said Rick Gaitskell, Professor of Physics at Brown University and co-spokesperson for the LUX experiment.

Dark matter is thought to be the dominant form of matter in the universe and WIMPs are among the leading candidates. However, they interact with other matter on very rare occasions and they have yet to be detected directly.

LUX consists of one third of a ton of liquid xenon surrounded with sensitive light detectors inside a titanium vessel. On the very rare occasions when a dark matter particle collides with a xenon atom inside the detector, the xenon atom will recoil and emit a tiny flash of light, which will be detected by light sensors. So far, LUX hasn't detected a dark matter signal, but its exquisite sensitivity has allowed scientists to all but rule out vast mass ranges where dark matter particles might exist. 

The new calibration techniques include injecting neutrons, which act as stand-ins for dark matter particles, into the detector, then track them to learn details about the recoil. The nature of the interaction between neutrons and xenon atoms is thought to be very similar to the interaction between dark matter and xenon. "It's just that dark matter particles interact very much more weakly—about a million-million-million-million times more weakly," Gaitskell said. He describes it as a "giant game of pool with a neutron as the cue ball and the xenon atoms as the stripes and solids." 

Additionally, LUX scientists injected radioactive gases into the detector to better understand its response to the deposition of small amounts of energy by struck atomic electrons. The LUX improvements allowed scientists to test additional particle models of dark matter that now can be excluded.

"And so the search continues," said Dan McKinsey, a University of California Berkeley Physics Professor and co-spokesperson for LUX and an affiliate with Lawrence Berkeley National Laboratory. "The latest run began in late 2014 and is expected to continue until June 2016. We will be very excited to see if any dark matter particles have shown themselves in the new data."

Planning for the next-generation dark matter experiment at Sanford Lab is already underway. In late 2016, LUX will be decommissioned to make way for the much larger xenon detector of the LUX-ZEPLIN (LZ) experiment, which will be filled with 10 tons of liquid xenon—three times the volume used for LUX.

"The global search for dark matter aims to answer one of the biggest questions about the makeup of our universe. We're proud to support the LUX collaboration and congratulate them on achieving an even greater level of sensitivity," said Mike Headley, Executive Director of the SDSTA.

The LUX collaboration is supported by the DOE and National Science Foundation (NSF). It includes 19 research universities and national laboratories in the United States, the United Kingdom and Portugal.