The dark matter experiment, Large Underground Xenon (LUX) completed its 20-month search detecting particles of dark matter and found none. LUX scientists announced their results Thursday at the International Dark Matter conference (IDM 2016) that was held in Sheffield, UK. But not findings are also findings: the LUX experiment is a milestone that will help develop future dark matter research.

The LUX detector is located nearly a mile underground below the Black Hills of South Dakota at the Sanford Underground Research Facility, inside a 72 thousand gallon, high purity water tank, that works as a shield to protect it from cosmic rays and other radiation that could interfere with a dark matter signal. LUX started to search for dark matter in October 2014 and finished the investigation in May 2016. The project has been supported by the U.S. Department of Energy.

A new calibration technique fired neutrons directly into the Large Underground Xenon 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. Credit:

The Sanford Underground Research Facility website quotes  Rick Gaitskell, professor of physics at Brown University and co-spokesperson for the LUX experiment, who said that LUX had delivered the world’s best search sensitivity since its first tests in 2013. He added that LUX collaboration pushed the sensitivity of the detector to a final performance that was four times better than the initial project goals and what they saw was consistent with background alone.

In spite of is remarkable sensitivity, the detector found no trace of dark matter particles. But the team is confident that the detector would have been able to find dark matter if it had passed through the LUX’s xenon targets. But even with no results, the experiment helps to rule out potential models of dark matter particles, and it will be used as a guidance to next dark matter experiments.

The leading theoretical candidate for a dark matter particle are the Weakly Interacting Massive Particles (WIMPs), and LUX was designed to detect them. The theory says that billions of these particles pass through the Earth and everything on it. The problem is that WIMPs interaction is fragile with ordinary matter, and it goes unnoticed, says the Sanford Sanford Underground Research Facility website.

But, what is dark matter?

Dark matter is believed to be part of the universe and the cause of its expansion, and it takes four-fifth of the mass of the universe. Scientists are sure it exist because its gravity is observable in the rotation of galaxies and in the way light bends as it travels through the universe.

Pulse Headlines reported last week that an international group of astronomers made a 3D map that shows 1.2 million galaxies and makes it possible to measure the expansion rate of the Universe and to calculate dark matter that forms the present-day Universe. But even with the map, LUX scientists have not been able to interact with it. 

Researchers say, according to the Sanford Underground Research Facility, that LUX represents one of the largest exposures ever collected by a dark matter experiment. During its 20-month run, it received nearly a half-million gigabytes of data. This was possible thanks to Brown University’s Center for Computation and Visualization (CCV) that used 1 thousand computer nods along with computer simulations at Lawrence Berkeley National Laboratory’s National Energy Research Scientific Computer Center (NERSC).

LUX: a complex work of engineering to reach complex sensitivity

The LUX detector is made of 1 third of a ton of cooled liquid xenon, surrounded by powerful sensors that were designed to find electrical charge and flash from WIMPs when they collide with a xenon atom within the tank.

The outstanding sensitivity that makes unique the LUX detector is the result of a series of calibration measures that seek to differentiate between dark matter signal and residual background radiation that is hard to block out from the experiment construction.

One of the calibrating techniques used neutrons which allowed scientist to quantify how the LUX detectors respond to the signal expected to be produced from a WIMP collision. To calibrate the LUX scientists also injected radioactive gasses into the detector to make it easy to distinguish between ambient radioactivity signals and dark matter signals.

All LUX calibration measures were made to help scientist to search for dark matter particles and to avoid confusion with other elements.

After LUX, what is next?

Mike Headley, Executive Director of the South Dakota Science and Technology Authority (SDSTA), stated that the search for dark matter aims to answer fundamental questions about the origin of the universe. He congratulated the LUX team for their research and continued saying that they are looking forward to hosting the LUX-ZEPLIN (LZ) experiment, reported the Sanford Underground Research Facility official site.

The LZ will replace LUX at the Sanford Underground Research Facility and instead of having one-third ton of liquid xenon, LZ will have 10-ton liquid xenon. The new experiment will also be fill in the 72 thousand gallon tank of pure water to avoid external radiation as well. The LZ will provide more sensitivity than the LUX experiment.

The spokesperson for the LZ, Harry Nelson from the University of California Santa Barbar, said that the LZ was possible thanks to the LUX experiment, and they expect the LZ to achieve 70 times the sensitivity of LUX.

The LZ detector could be working in 2020.

Source: Sanford Underground Research Facility