The U.S. Department of Energy has given the green light to the LUX-Zeplin (LZ) experiment, which wants to help figure out dark matter, an invisible substance that must make up a lot more of the universe than visible matter does. It is essentially a scientific placeholder because whatever it is should explain a number of important behaviors of the universe, including the structural integrity of galaxies.
LZ's approach posits that dark matter may be composed of Weakly Interacting Massive Particles – known as WIMPs – which pass through ordinary matter virtually undetected. The experiment aims to spot these particles as they move through a container of dense, liquid xenon. That container will be surrounded by a tank of water, along with an array of sophisticated light sensors and other systems.
"We emerged from a very intense competition," said Daniel McKinsey, a Yale professor of physics. The ongoing LUX (Large Underground Xenon) experiment looks for dark matter with a liquid xenon detector placed 4,850 feet below the Earth's surface. The device resides at the Sanford Underground Research Facility, in South Dakota's Black Hills, a played-out gold mine.
Putting the device down a mineshaft weeds out cosmic rays. Gamma rays and neutrinos, however, still will be able to seep into the device. They'll be like tiny bowling balls, careening into the liquid xenon and colliding with electrons. Those collisions will be identified and factored out.
The researchers hope that the remaining collisions, the ones involving nuclei, will identify the presence of dark matter. "It comes down to distinguishing between electron and nuclear recoils," McKinsey said.
LZ will be a meter taller and significantly wider than its predecessor. The amount of xenon will jump from 250 kilograms to 7,000 kilograms. Such considerations become critical when you're conducting research in a mine,
"We have the most sensitive detector in the world, with LUX," McKinsey said. "LZ will be hundreds of times more sensitive. It's gratifying to see that our approach is being validated."
LZ is an international effort, involving scientists from 29 institutions in the United States, Portugal, Russia, and the United Kingdom. The DOE's Lawrence Berkeley National Lab manages the experiment. The goal is to have it operational in 2017, while continuing work with the LUX experiment.
Two other dark matter initiatives also earned support. Those are the SuperCDMS-SNOLAB, which will look for WIMPs, and ADMX-Gen2, which will search for axion particles.