Background interference. It’s one of the biggest issues researchers believe is hurting their chances of detecting dark matter. This week, one team of researchers announced they have increased the sensitivity of their detector, the Large Underground Xenon (LUX) experiment. LUX is an 815-pound vat of liquid xenon in a former gold mine located under the Black Hills of South Dakota.
Detectors around this vat of liquid xenon are on the lookout for flashes of light created when xenon nuclei are struck by weakly interacting massive particles, or WIMPs. These WIMPs are one of the leading candidates for dark matter.
“We look for WIMPs produced in the Big Bang that are still around, up to very high masses – we have the best sensitivity of any experiment to date for WIMP masses above four times that of a proton,” said Daniel McKinsey, a professor of physics at the University of California and a spokesman for LUX. “We haven’t yet observed dark matter interactions, but the search goes on.”
New improvements to LUX
Bottom-up view of the inner LUX region, showing the top array of 61 photomultiplier tubes. Credit: Flickr/LUXDarkMatter
Tuning out background interference is a must. The latest techniques center around calibrating dark matter signals and filtering out bogus collisions caused by cosmic and gamma rays. Being under nearly a mile of earth helps shield LUX from most cosmic and gamma rays.
Researchers bounced neutrons off the xenon atoms to see how the LUX detector responds and calibrate it to hopefully detect dark matter interactions with xenon. These interactions would be “about a million-million-million-million times” weaker than neutrons according to Rick Gaitskell, a professor of physics at Brown University and co-spokesperson for the LUX experiment.
Researchers also injected a pair of radioactive gases (tritiated methane and krypton) to help separate signals produced by common events with a potential dark matter signal.
“It is vital that we continue to push the capabilities of our detector in the search for the elusive dark matter particles,” said Gaitskell. “We have improved the sensitivity of LUX by more than a factor of 20 for low-mass dark matter particles, significantly enhancing our ability to look for WIMPs.”
LUX’s hunt for dark matter began in late 2014. Since then, it has been operating 24/7. In about six months (June 2016), LUX will end its current run. The Sanford Lab (which runs LUX) is already busy planning for the next dark matter experiment. And researchers are going bigger, much bigger. LUX’s 815-pound vat of xenon will be traded in for 10 tons.
The much larger xenon detector will be known as the LUX-ZEPLIN (LZ) experiment.
LZ spokesperson Harry Nelson from Santa Barbara puts the next-generation dark matter experiment into perspective.
“The innovations of the LUX experiment form the foundation for the LZ experiment, which is planned to achieve over 100 times the sensitivity of LUX,” said Nelson. “The LZ experiment is so sensitive that it should begin to detect a type of neutrino originating in the sun that even Ray Davis’ Nobel Prize winning experiment at the Homestake mine was unable to detect.”
Dark matter may continue to elude researchers, but you can’t say they’re not trying to find it. We may just need a bigger vat.