LUX: The end of an era

Five years ago, the Large Underground Xenon (LUX) experiment began its long journey to the Davis Cavern on the 4850 Level of Sanford Lab. Results published in 2013 proved LUX to be the most sensitive dark matter experiment in the world. When LUX completed its 300-live-day run in May of this year, the world learned LUX was even more sensitive than previously determined. 

Earlier this month, the LUX collaboration began decommissioning the experiment. "It's bittersweet, the end of an era, but it was time," said Simon Fiorruci, a LUX collaborator from Lawrence Berkeley National Laboratory.

"The detector delivered everything we promised in sensitivity and then went even further," said Rick Gaitskell, physics professor at Brown University and a co-spokesperson for LUX. "So there is great pride, but also sadness to see an old friend being pensioned off. Of course, the success of LUX acted as an important pathfinder for the larger LZ experiment."

LUX-ZEPLIN (LZ), the second-generation dark matter detector, will hold 30 times more xenon and be 100 times more sensitive than LUX. It will continue the hunt for WIMPs, or weakly interacting massive particles. The top prospects for explaining dark matter are observed only through gravitational effects on galaxies.

"The nature of dark matter, which comprises 85 percent of all matter in the universe, is one of the most perplexing mysteries in all of contemporary science," said Harry Nelson, LZ spokesperson and a physics professor at University of California, Santa Barbara. "Just as science has elucidated the nature of familiar matter, LZ will lead science in testing one of the most attractive hypotheses for the nature of dark matter."

LZ recently received approval from the Department of Energy that set in motion the build-out of major components and the preparation of the Davis Cavern. But to make way for the new experiment, LUX must be completely uninstalled?with the exception of the water tank in which LZ will be housed. 

"Essentially, we have to do everything we did to build the LUX detector, but in reverse," Gaitskell said. 

But decommissioning isn't as simple as pulling the detector vessel out of the 72,000-gallon water tank in which it has resided for four years. The team first had to remove the 370 kg of xenon and prepare it for transport to SLAC National Accelerator Laboratory. Then they disabled the support system and disconnected thousands of cables. Next, the detector was removed from the water tank and readied for its trip to the surface. The vessel will be opened and the parts analyzed for possible use in LZ. 

"By March we should be removing the last table and chair and handing the space over to LZ," Fiorruci said. 

Construction of LZ will begin in 2017. Operations are expected to begin in 2020. "And so, the process of build, operate and deconstruct begins again," Gaitskell said.