In an abandoned gold mine inSouth Dakota,physicists are building a way to test for dark matter– invisible particles that affect theexpansion of the universe.
The Large Underground Xenon Apparatus (LUX) is a collaboration of seven universities,including UC Davis.Physics professors Mani Tripathi and Robert Svoboda are designing part of the experiment that will be transported fromDavis toSouth Dakota.
“Our role is that we are helping to build part of the instrument itself,” Svobodasaid.
Dark matter got its name because though it has a gravitational force,it is not visible to humans.The name is also a pun,because the particles are a mystery to physicists,said Hitoshi Murayama,professor of physics at the Lawrence National Laboratory at UC Berkeley.
“We are in the dark when it comes to understanding it,” Murayamasaid.“What we have learned recently is that this dark matter is something totally different from atoms.“
TheLUX apparatuswill use600poundsof liquid xenon suspended in25-foot-high tank of water to test for particles of dark matter.The tank of water will shield the detector from gamma rays and neutrons from the surrounding rocks.
The test site is located4,800feet underground in the Homestake Mine in Lead,S.D.The rock and earth above the mine should filter out all outside radiation except dark matter,which passes through matter– including humans– daily without effect.
“Dark matter is sort of ghost-like.It can go through the Earth with no problem,” Murayama said. “It can sort of sneak in.“
The theoretical dark matter particles are called WIMPS,an abbreviationfor weakly interacting massive particles.If WIMPSexist,then they should give off a flash of light when they bump into the nuclei of the xenon atoms.
The top of the xenon-filled basin will have a meshcoverwith5,000volts of electricity racing across it.If dark matter hits the xenon,it will knock electrons off the xenon atoms.The electric mesh will suck the lost electrons up into the detector.
Murayama said that though the race to show the existence of dark matter began in the’80s,new technology,like the LUX,isfinally giving physicists a chance to test their theories.
“These experiments have technologically advanced to the level where they can realistically hope to find dark matter,” Murayama said.
A hurdle facing dark matter research is the need to eliminate all radiation in testing sites.The LUX needs to be able to test for dark matter radiation with no outside interference.Svoboda said his team is working on a way to keep the testing apparatus clean– this means not even a fingerprint smudge.
“Fingerprints are radioactive,” Svoboda said. “Our sweat has salt in it,and when we touch things it leaves a smudge of radioactivity.“
The National Science Foundation and the U.S.Department of Energy have allocated$1.2million to the LUX.The LUX is a low-budget project compared to the Large Hadron Collider being built at theEuropeanCenter for Nuclear Research nearGeneva,Switzerland.The Large Hadron Collider may also be used to test for dark matter.
The Homestake Mine,a former goldmine,was chosen by National Science Foundation.Themine will also be used as a deep seismic observatory andforresearch regarding the percolation of water in rocks.The mine is currently being drained of all water,and the work on the LUX should begin late summer or fall.
MADELINE McCURRY SCHMIDT can be reached at campus@californiaaggie.com.XXX
